Hi welcome to Tear down! Tuesday We got another vintage bit of gear today and it's from a cowb. something you wouldn't ordinarily get your hands on. It's a resistance transfer standard. It's the Fluke 5450 A straight from the mid 80s I think 85 86 vintage something like that.

This would be the transfer um standard used for calibrating Uh multimeters back then. it's OB now. But uh, you know it's still not a bad bit of Kit And look at the size of it. It is absolutely enormous and uh, uh, designed to either go into a rack or be uh, bench mounted like this.

And basically it is nothing more than a bunch of precision resistors in a box. That's pretty much all it is. Yes, it's got a big lead display on here which shows you the value, but it doesn't actually uh, measure anything. All it is is basically a bit of automated gear for automated testing of Uh multimeters in a typical calibration lab.

And the way it works is, um, it's a four terminal uh, capability, two or four terminal measurement. It's got uh, really? Shmo Precision resistors inside. and when you calibrate this thing um itself, then you actually program in the exact value of the calibration resistors in here. So this doesn't actually measure its own internal resistors.

It can't actually do that, but what it can do is actually display the value. Um, what use is that I hear you ask? Well, in automated measurement with the upside down, all the electrons are going to fall out Gpib on the bottom. You can automate the testing. This and it can read the value out of this to know exactly what value the calibration resistor is in here and then it canare it with the device out test and so on.

So it's a really just a very fancy automated Reay switching box and it could be interesting inside not only in the Uh type and construction of the Precision Uh resistors calibration reference standard resistors in this thing. but uh yeah, in the way physical construction and stuff like that keep out noise leakage. all that sort of stuff in the analog section of it could be really interesting. So you always say on E blog, turn it on, take it apart and if we take a look at the specs here for it, I mean it's you know, compared to uh, sort of modern multimeters.

Um, it really wouldn't be uh suitable for, say, calibrating a modern well I don't probably not. Anyway, calibrating, say a Modern Agilant, 3461, A6 and2 digit multimeter or an equivalent digital multimeter I mean we're looking at, you know, nominal tolerances here of 5050? PPM uh, something like that, that absolute uncertainty is actually quite good. You know, down in the order of Uh 5, PPM or under for like 24 hours or 1 year, you know, 1230 uh, PPM and uh, they're the various Uh test currents. but you know, compared with say my uh Precision resistor uh box I've got here which has just got a couple of $20 resistors in a modern, uh modern vet resistor.

There's the Uh part number. Let's get the best one here, which is the 10K one. You know we're talking 05% or 50 PPM accuracy. So it's sort of.

you know in the same order as this. and if you compare the stability like for example, a 90day s, you're only talking, you know 3 PPM or something like that. Really quite good and temperature coefficient here 1.5 PPM per degree C And if you compare that to here, this is like you know 2 PPM per degree C So you know it, It's not a huge amount better than just a modern uh, you know prec prision uh resistor from the likes of Vishe that you can buy for like $20 Odd. but you know in practice I'd bet my money on the resistors in this box any day of the week.

So this is basically a single-purpose resistance uh, calibrator only designed for calibrating the resistance or calibration, checking the resistance ranges of multimeters. That's it. Doesn't do anything else unlike, you know, modern multi-function calibrators that can do everything you know ACDC uh, voltage, resistance, current, all sorts of stuff like a Fluke 5700 or a 50a multifunction calibrator for example. So they they're pretty much uh, made something like this, uh, obsolete.

I'm not sure of a cow lab that would still be running uh, one of these things, a 54508. but if you are aware of any CBS still using them for a specific uh purpose, please chime in. But uh, yeah. Basically, here is the Uh control panel for it.

It's designed for two and four wire measurement. It's got a two wire compensation function which basically just doesn't do anything fancy. It just adds a uh, a pre-entered pre-measured and pre-entered value on top of the actual internal calibration uh, value in there. So it just adds a stored number uh basically to the value.

And of course, in four wire mode, you would just hook this directly onto your multimeter. The Sense wires go to the sense terminals your multimeter, the output goes to the input terminals of your multimeter. That's it. It's also got a ground Shield which you can turn off and on external guard for when you're actually calibrating this thing.

and I won't go into the whole uh way. You would actually calibrate this in terms of uh, shielding, and everything else, but can be really, really important that external Uh guard Shield That's just not just Ms Earth Willy-nilly it's you know, has very specific uh requirements in terms of noise reduction for calibrating this thing. and then all you do is you just choose your range and that's it. Um, it's pretty basic.

It's got a Uh multiplier so it can only uh, select values of 1 ohm, 10 ohms, 100 ohms in each decade, up to 100 megga ohms. but you can actually multiply that by 1.9 So if you wanted a 1.9k standard resistor, press that button with that one and you would get 1.9k it' switch the relays internally, clunk, clunk, and you'd get 1.9k reference resistor across there and that's pretty much all ARS to it. It also allows you to display the PPM error, but once again, it's not actually measuring anything. it is just displaying a pre-recorded value in there and that's all it does on the Uh 2, 4, 6, 8 digigit uh display.

Here it can show the Um output value uh, or the percentage error for there and that's all there is to it. As I said, it's dumb. this display is not reading anything, just showing you a pre-stored value on the back. Nothing fancy, of course.

Mains Input: um I E48 uh G Gpib standard plus a set of Uh rear terminals on the back for when it's uh mounted into a rack or something like that. Once again, these are really going to. these are low EMF uh connectors in there. You can see they're probably some sort of uh, a torium, copper or something like that.

really? Schmo I Don't know what are they worth? Like a hundred bucks each to get a replacement set of those and it's made in the United States of America still has the calibration uh, void seal intact um, but the thing has been uh opened. As you can see it, uh was calibrated by the fluke Metrology Lab. but uh, it, has been opened. So inside this thing um, is going to be I think when we open it up, we're not going to find anything fancy at all.

Uh, we're just going to find some uh, a whole lot of digital stuff which of course drives the Um Gpib and the Seven segment displays on the front front. Um, nothing doing there that has you know, nothing to do with the uh, actual real operation of this unit. What we're interested in is all the uh, the uh Precision reference resistors in here and the relay switching and all that. that will be probably triple Shield or something ridiculous like that.

and uh, it will probably be laid out quite well because this thing, you know, if you bre if you open this thing and you breae on it, um, you know you're probably going to have to recalibrate the thing I mean especially when you're talking or if you touch it, you know all the grease in your fingers and stuff like that. Probably not if you breathe on it, but you know the oils from your fingers if they get on and contaminate the analog board in here. Oh, here we go. Yeah, contaminate that analog.

Aha. Tada Look at that and there it is. Check that out. It's actually quite big.

I've had to uh, prop the thing up vertically on my bench here to take a look and uh, as I was saying, um, the uh oils and stuff from your fingers if they contaminate the analog circuitry in here as I said You know here it is behind all the Um shielding in here. Leakage sensitive printed circuit assembly use special handling. There you go because when you're talking about 100 Meg you know a Precision reference resistor. which is you know, 05% accurate or something.

It doesn't take much in terms of leakage for that value to change. All right, let's just pluck a number out of our ass to see what sort of scale magnitude we need to get in parallel with our 100 megga reference resistor. For you know it to start being a problem I Chose my Casio FX 61f because it has a parallel button the only commercial calculator in existence that ever did I think oh beautiful. Anyway, um 100 Meg in parallel with let's say 100 Gig 100 Gig Ohms Okay, let's have a look what we get.

Look at that. 99.9 Meg We're still outside of our tolerance and if we go divided by 100 Meg Like that there we go. subtract one and uh, let's shift that and times 100 what do we get in percentage? There we're talking. you know, 0.1% Okay, so that's is.

you know, outside of our 05% or better, just just forget about it. So even 100 Gig ohms in parallel with uh, that 100 Megga ohm reference resistor gives us that .1% error. Way out we need something in the order of, you know, even like Terra Ohms, Even a one Terra Ohm can actually affect this thing. And of course that's aide from noise issues I Mean we're at 100 Meg at 1 Vol you're only talking 10 nano amps I Mean you know it's go.

It's na all half a bees dick. So really, any noise that gets into this thing can be a real pain in the ass. That's why that um, switchable Earth terminal on the front panel is such a big deal. So this is really interesting.

They've actually got a relay table here which shows you which relays are energized for each of the particular ranges. A Reay maap. Look at that. That's just gorgeous engineering right there.

So it's 34 re inside this thing and it even gives you the fluke part numbers for the different Uh Reay types there. We've got ourselves what looks like the Uh Transformer box in here and uh, the internal voltage selections are in there and look at this thoughtfully provided two spare fuses in little holders on the side. Accessible. Ah, it's a thing of beauty.

and really, there's nothing, uh, exciting in there at all. Um, we've just got some Uh range selection switches for the mains range. and there's the mains Transformer down there. But you know the main point is, it is inside its own shielder box.

They're not taking any chances and as far as the digital board goes, well, our care factor is around about 0 plus 50. PPM I Mean it's not that exciting at all. We've got a Z80 CPU uh down here and we've got some rums and some memory. and well, whoopy do I mean all it's doing? Um, there's some jumpers down there.

That's some programmable jumpers. but really, you know we don't care. Ribbon cable going off to the uh front, um, uh, lead, uh, Matrix uh display. and really, we don't care.

You don't need much horsepower at all to drive a Gpib. and uh, then you know, drive a display and store a value. So check out that monster Mains filter cap though. that's absolutely insane.

Manufactured by Uh. Sprag Computics. Um, jeez, Sprag, Are they still around? I Don't know, but that's a 22,000 microfarad 15 volt cap plus 85 C rated. Jeez, look at the size of it.

What the hell do they need that for? It's absolutely enormous. Uh, for the Relay switching I Guess klunk and we have ourselves a date code. Well, it's actually 1970s look copyright 1970 9 John Fluke Manufacturing Co So this model dates at least back to then. I Mean the user manual I got says I double checked out 1984.

It doesn't say anything. uh, less than that. But uh, we've got ourselves a date code we're looking at. you know, 1989 Uh.

vintage? that could have been changed, but look, you know we've got 88 Vintage Parts Bit of dust on this sucker. But yeah, so this thing was manufactured in late 80s. Um, you know, 89 maybe 1990? All right, let's lift the skirt up. This is what we want to see I better not breathe on this thing.

better not sneeze because uh, we could be in trouble if I do that I definitely won't be uh touching anything inside here I have a poke around with the uh plastic stick I Was wondering why there's a hole in there. Well, the hole is a finger lift. Look at that. There we go and I'll try not to spit when I talk to I Try not to get too excited and salivate over this thing.

Here we go. Tada Holy doly look at that. Oh, look at those reays. Look at the resistors if we take a look at the reays here.

Company: I've never heard of Potter and Brumfield who to Google Sure enough, Potter and Brumfield still exist, but well, the brand uh does. but it's now owned by TE Connectivity And yes, they still make reays go figure. And as we've saw before on the front panel, there are various types of reays in here. This one is a 4.5v Dc1.

um yeah. double pole, double throw is it. And on the analog board, we've got ourselves copyright 1983 and down here we got ourselves a bunch of um, unusual looking Coto Reed relays of course Cotto One of the Uh Best Brands in the business in terms of uh, you know, low leakage, high performance uh relays and these would spe specifically be low leakage types Had a quick look of a data sheet, couldn't find the exact one but I found a 1240 series 1 uh contact leakage in you know, up in the order of uh Power 10 the power of 14 and I think I've done a video Way Way Back on Uh relay matrices for measuring uh, high value resistors I will try and find that and Link it in and now Precision resistors in this thing. Check them out.

They are manufactured well I assume they're manufactured by uh, fluke. They've got um, individual, uh part numbers. Well, fluke part numbers I presume and look, they've got two in this case uh, 40.5k uh 05% Um, you know I technology I don't know some sort of wire wound and the 05% does seem to be the best that they've got in here we can see, but some are you know 0.01 The ones that you know aren't as critical. Cool.

There's another couple up there 0.01 uh 05 for 4K 1es 1.8k Once you get down in those values 0.1 there's another 162 Ohms for example. and here we go. These low value are 40 ohm ones 05% each. But take a look at the configuration.

what we've got here is uh four paralleled uh 40 ohm resistors. so that gives us a 10 ohm better than 05 5 uh% And then that 10 ohms in series with another uh 10 ohm there. And then we've got a then that is in series with 262 Ohms in parallel and check out the configuration. It's uh, you know, it's all over the shop.

They got some complex Arrangement here, that's for sure. And then we've got some 280 Ohms in parallel. and then we've got uh 1.62 K here. and then that's branching off there and no, and then 1.8k So this really long string of precision resistors look at that isn't that pornographic special low leakage codo relays.

Well, of course, on the uh, very high side resistor values. This one is uh oh, you probably can't see that, but that's Um 81 Meg There it is. and it looks like that is. You can check the arrangement down in here of this uh string with the relay switching in there and they're 4.5 Mega pop.

And these ones here are yeah, these are all 4 1/2 Meg getting down to 450k here. So this part of the circuit is where our leakage really matters. and you can see that they've conveniently marked the Uh tap points I Mean, there's the 19 Meg tap there. So when you include that 1.9 multip, When you switch that button on the front for the 1.9 multiplier, there we go.

That tab for the 10 Meg range. That's the tap it's going to use. And then there's the 10m uh tap there and so on. down the string.

There's the 1.9 Meg tap. There's the 1 Meg tap and you can bet your bottom dollar that they know the leakage of this board down in here. and the uh uh solder. It's got that crinkly, uh, solder resist coating on it.

Fluke. Really would have done their homework on that. You can bet your bottom dollar. But of course, when you get to the really top end of the range the 100 Meg the PCB itself is not good enough.

You get too much leakage. What do you have to do? You have to have uh special low leakage insulators like that with uh, the uh copper removed from around there and then you have to run insulated pointto Point wires like that right into special output relays like this. They couldn't. Those Cotto ones that we looked at weren't even good enough.

These are electrol brand ones. W Look at those. How much do they cost each? or did cost each? There we go. Electrol brand another one I've never heard of.

um R 8538 Couldn't find any uh info on that on a first pass except that uh Electro were bought out by Hamlin so you know I'm not sure if you could still buy those, so check it out. We've got the input coming over here. switching through here once again on these isolated standoffs here. all point to point wiring.

They cannot use the PCB this wire down there is sneaking off through a hole in the board. Not only air is good enough for this, and for those who love their connectors, look at that low EMF tum copper no doubt. And in all the excitement over the pornographic reays I Missed this little cludge. look at this.

a 7805 linear regulator That was supposed to just probably be freestanding in the board there. or maybe um, you know, attached to the uh back panel there they've M Look, it looks like they've done a staggered offset. Maybe they didn't get the PCB right to line up with the shazzy or vice versa. So they've I don't know, they've done a cludge there, mounting it up off the board and uh, there's a there's a seal pad in there to insulate it uh, from the back, but jeez, look at that and they've done got to the trouble to add a flat Flex there.

Unbelievable. I Mean it's not a huge amount of current obviously, but you know your guess is as good as mine who goofed up there so you can really see the arrangement of the resistors here. I Mean here's our 10 Ohm tap 9 Ohm tap 100 Ohm tap 190 Ohm tap uh and so forth up there blah blah blah goes around like that comes down here like this. but what I don't see is, well, there's our com that that says com down there.

There's a common terminal but I don't see the 1 Ohm tab. it's not there. and if you're curious, uh 10 ohms the spec for that or the nominal tolerance is Uh 500 PPM or uh 05% Um, in terms of absolute uncertainty, we're down to about you know, 4050 PPM something like that. So that's basically to get that 05% we're looking at 5 milliohms uh, maximum error there.

So in terms of you know, relay switching going all the way through the wire into the front panel and all that sort of stuff. Um, that stuff. Well, it doesn't have to be better than that. But in terms of the Uh, you know the stability I mean you can calibrate the uncertainty out of all that.

but um, you know. Still, it's got to be very, very low. These relays have to be ultra reliable in terms of uh contact resistance. So I don't have the Uh schematic for this one to hand.

If anyone does, If anyone actually has the service menu which has the front end schematic in it, then that would be fantastic. The uh, actual, you know, so we can see the actual relay Arrangement wouldn't surprise me if they you know paral paralleled up some relay contacts or something that like that for these really low order ranges I Can't imagine where the 1 Ohm range is. actually haven't found it yet H Shielded can wonder what's under there. Silly me.

I did find the schematic in the Um in the operational manual for this thing was right at the back I swore I checked it and it wasn't in there, but duh, it is. and Tada Here's the schematic for the Um analog section here, with all the relay switching and the wiring and everything else. Fantastic. All beautifully handrawn as you got back in those old days.

So let's take a look at the string here. Here we go. Here's our 1 Ohm resistor and our 1.9 Ohm resistor up here, which we haven't found yet I bet they're under that can for sure. And there you go.

There's the four paralleled uh 40 Ohm resistors that we got before and then all the various uh points. There's our common terminal, so that's sort of on the so these lower value resistors are on the flip side of that. and then we went up the chain, went up the chain, and we can switch various configurations of these resistors through to a high and low bus. very similar to what I've done in a um, a previous relay switching Matrix which I said I'll link in and I'll try and do that um and going all the way over to our final output and check it out.

there we go. Sure enough, they've identified on the schematic look. they've put a circle around that which indicates to the PCB designer you know that is to be marked off the PCB I'm not sure over here number one so we're obviously got some detail we'll have to look at. but uh yeah, that indicates that that's raised off the PCB and this is all just wiring.

And there we go. They've got 4401 cable. they're specifying the type used over there. so all these high impedance uh parts are all mounted off the board and it looks like I might be right in that they do use multiple Uh relay contacts in parallel for the 1 and 1.9 Ohm ranges.

Check it out There we go three in parallel on each line just to get that contact resistance down and to within a manageable, uh, you know, tolerance variation over the switching life of the Rel. There you go. unless noted. Otherwise, there's our note for our points down there.

Here we go: Teflon Standoffs There we go. seven places. Resistors are specially match set. There we go R5 to R39.

So R5 Yep, all of these R5 through to R. Well, R5 R6 Yes, all of these are specially matched. So yeah, they don't just roll off the assembly line. They're probably individually hand tested.

hand. uh, you know, hand measured and sorted by. You know, someone rubbing their Gray beard as they do it, sorting them into the individual bins and then you know, putting a bit of spit and polish on each one. Oh beautiful.

And you can see the beautiful soldered ends of the cans of those resistors there. Ah, just absolutely beautiful goldplated pins. Oh, each manufactured and hand assembled by nude virgins in Utopia land. Just beautiful.

If anyone knows if Fluke actually uh made these resistors themselves or still do roll their own specialty resistors, please let us know. So I reckon the Uh one? what is it? The 1 Ohm and 1.9 Ohm resistors are under this can down in here. Does it have an extra Reay down in there? I Don't know I haven't looked at the schematic yet? Dare I Open this sucker. It's almost sacriligious, isn't it? It's just oh, oh, couple of big standoffs on there and uh yeah, I mean as I said, you know, even at the 10 ohm range, only talking what was it? 5 milliohms or something to get within that 05% band and uh, really, it's even going to be.

well, it's an order of magnitude actually less for oh, look at those Yes wire W resistors on card. Look at that now. I'm sorry that it's not easy to get in here, but look at the wire W resistor that looks like one big wide strap on a clear. you can actually see through it.

You can see that's like a some sort of uh, you know, a perspect, uh, you know, acrylic sort of uh uh sheet that they've wound that on. but you can see that that's tape wrapped over there and look individually serial numbered down in there. Oh yeah, these things are definitely manufactured by nude virgins in Utopia land that's for sure and individually tested by gray beards, no doubt. Look at that.

Beautiful. They would have been manufactured inous by Fluke I'm guessing and check out the Dual terminals coming off that thing both there and there. On that side, they've just tapped these off individually right at the point there? Beautiful. Yeah, so that's probably some form of uh, nichrome resistor.

Uh, well, you know, wire as in like a flat um, strip wire and they've just wound that around that uh, plastic seethrough former there and then they've just solded. Sorry, it's very difficult to get in here, but then there we go. You can see the strap coming over and then solded directly onto that, uh, dual point contact there. One of the interesting things to note is that they have socketed all of these um, low value relays.

By low value I mean used on the low side of the resistant low value resistance side of the reference. uh, string in there I I Would have thought that wouldn't have been the go. You would have sold of these directly onto the board, but um, that certainly makes them replaceable. And I'm sure those sockets are worth a fortune and goldplated to the hill and you might be wondering why it was shielded like this.

Well, this sucker is a coil in there. You don't want anything getting in there because as we saw before, these are Precision wire wound resistors. These are already uh, shielded on one end of the can there. So once again, it's interesting to see the progression in the contact and resistor technology as you go up right down at the low end here.

special Shielded wire wound. you know, hand manufactured wire wound resistors down in here, and uh, multic contct relays down in here to ensure the Uh tolerance of that. And then we've got some fairly beefy ones for the low value resistance on the Precision string along here. So once again, you really need good, top quality low contact resistance reays.

possibly multiple contacts along there as you go up, you know, in the tens of ohms, the hundreds of ohms sort of range. And then as you get up into the Kiler Oh range, you can go for these, uh, smaller contact resistance. Uh, by smaller I mean physically, uh, smaller relays. So you know probably not as greater or as lower contact resistance as the other relays along here.

not nearly as critical on these lower ranges down here. And then you get up to these Cotto Re relays on the sort of the Meg Ohm range up here where contact resistance doesn't matter at all, it's down in the noise. You can't even measure it. What matters right up at this end is the insulation resistance of the relay, which wouldn't have mattered for all these ones down here.

Who gives a rat's ass what the insulation resistance of these relays is when it's in parallel with you know, 1 Ohm 10 Ohms hundreds of ohms. But when you're in parallel with, you know, 10 Meg 100 Meg Things like that as I said, you know ter ohms uh, gig ohms You hundreds of gig ohms up into the Tera Ohms region actually matters. So that's why you need those very high, um, insulation resistance values up here. from contact to contact.

You know, in terms of uh, up to up to the point where it's not necessarily the relay that dominates, it's becomes the PCB that dominates itself. the surface of the PCB As I said you, you know, oils from hands, contaminants from the air, other stuff. There's no fans in this thing. so um, you know nothing's actually uh, blowing through this thing, but dust has accumulated.

Uh, to the point where down in this section, with the really high values, we needed more special relays. read relays again, and then that Teflon standoffs on the board so we can't rely on the PCB anymore. right up at the high end and that as you progress all the way through, you got different challenges at each design stage. Fantastic! So I hope you found that, uh, rather interesting.

I certainly did. And you know there's more technology which goes into actually designing an analog section like this for one of these Precision uh, Precision calibrators not only just designing, but manufacturing the Precision resistors themselves. And uh, as I said, if anyone has any info on manufacturing, fluke, manufacturing their own Precision resistors in here. Uh, please, let us just know.

So there you go I Love looking in high-end gear like this. You always find nice little uh, you know, design tweaks here and there to get these things. Um, you know, to get the operational performance of these units and this isn't even bleeding edge these days. I Mean this is late '70s You know, early to mid 80s technology designed to calibrate multimeters of that era? You know it.

It's probably maybe not even good enough to uh, you know, calibrate a modern 6 and 1/2 digigit multimeter like uh, the Agilant one I've got there. So there you go. Unbelievably fascinating I Love this sort of stuff and if you want to discuss it, best place to do it is the Eev blog Forum link below. As always, I'll link in any available Uh data sheets and the manual for this thing which has some beautifully drawn uh, circuit diagrams for this thing.

Uh, in terms of like all the digital stuff, all hand drawn, just beautiful really is I Love it. And here it is working. connected to my Agilant 3461, a 6 and 1/2 digit bench meter and it hasn't been warmed up for long. but it doesn't seem to drift.

Uh, well, neither of them seem to, uh, drift much at all. really. So um, this is on the 1K so as you can see, it's uh, got uh programmed in as the calibration value is 1.66 K and we're reading 1.86 not quite. uh, bang on, but you wouldn't expect it based on the Uh tolerance and I can uh change the range there and you can see it seems to be on the high side for uh, various? uh I can go Auto Range here, but often it doesn't quite get the auto range quite right and as you can see, this always seems to read on the uh high side of things and point there, you know there it is 10 Meg Oh, that one's reading actually lower than what we're getting on here, but as you can see a bit of noise on there, probably have to do some extra uh Power Line Cycles and at 100 Meg it's reading low.

but on most of the Uh low ranges, it uh, certainly seems to be measuring um slightly. on the high side I think that one's almost bang on if you see the Auto Range doesn't quite work when it's on this thing when it's quite when it's right near to the full scale there. so we can actually change that. There we go, that one's reading slightly, but most of the mid-range stuff seems to be reading slightly high.

Now we're getting into tricky real tricky business down in the Uh 10 ohm range down in there. but uh, as you can see, it's um, still within spec. Let's take Uh 1K Well, you know it's it's within margins of this entire uh uh test set up. Let me give you an example here.

Let's um, do this one and see how far we're out in terms of uh, percentage. So we're looking at 1. 85 for example, divided by 1.66 and we're looking at that. subtract one, Change the register there and we're looking at uh times.

Change that to percentage and we're looking at um, you know, round about o uh, let's say Point round it to 0.02% or 20 PPM and that is with that is better. The difference there, roughly 20 PPM or .2% is within the 24hour accuracy spec of my agilant bench meter here. So as you can see, um, you know which one's right, which one's wrong? Uh, you know where? We just don't know. we would have to, uh, take this to a standards cow lab that has an order of magnitude or better better than this agilant unit, and certainly, um, at least maybe four times better say, than this unit itself to actually have it recalibrated I it doesn't have a cow sticker and I have no idea when it was last, uh, actually calibrated and these values actually programmed into the thing? Have no idea.

So who knows? it may not. It might have been 10 15 years ago I Don't know. It might have been a couple of years ago. Got no idea.

Anyway, it does, uh, work. but hey, um, because the resistors are Ultra stable in this thing. Um, we could just have this re recalibrated. We just hook it up.

Take it to standards C Lab programming the new values and bang I'm sure it's not going to drift a sausage. so as always, if you enjoyed it, give it a thumbs up. Catch you next time.