Thanks ivan747.
edit:I don't understand your first question: "1µV resolution or 1µV full range?"
I just want to trust what I get, even if I need to use a calculator.
This is exactly what I believe I'm looking for. Great price:Value ratio!
I'll jump on it after a few more questions.
...In my mind, 1µV is about on the same level as Voodoo. 
(No experience= No understanding)
How important is it that I get a "tested" unit?
Are these units affected by atmospheric changes?
Is there usually a "field/self calibration" routine on these or something?
(I can also run a calculator pretty well if you know little math "self checks" that you can walk me through)
About leads:
Do I need $$$ leads or are they going to be pretty much the same for my needs?
How much will resistance in the leads affect the 1µV resolution?
Is there an offset I can compensate with? (or can I program it in?)
Thanks guys! I really appreciate it!
Frito
edit: I skipped ivan747's first question 
...oops, my bad. fixed.
Well, there is a difference between resolution (which is fomally called sensitivity) and the maximum value that the instrument can display. I was asking if you needed something that can go down to 1µV (so that is can read down to 1µV) or something that's so sensible that is only goes up to 1µV (which is really rare, if not economically impossible for us enthusiasts).
I assumed you want 1µV
sensitivity, also known as resolution, so I got you a list of benchtop multimeters you could buy used.
Okay, now, calibration.
You instrument being in "cal" or calibration means, in the end, that your instrument reads the voltage/resistance/current/whatever within its margin of error. There is a LOT of more stuff to know about calibration, but I'm not an expert in this topic, so I don't want to misinform you. There are plenty of guys who do know that are watching this thread and could help me out
When measuring 1µV resolution you might have to deal with noise. It's simple to get rid of noise. There is a Null button on practically all multimeters. If you short your probes and still see a reading (for example 000.003mV) you hit the Null button and it makes that reading zero. If you are measuring really sensitive stuff, you might also want to use a BNC cable or a twisted pair of cables. You only have to get a pair of BNC to banana plug adapters in the case of BNC. For a thermocouple I'd probably use twisted pair. The idea with twisted pair is that the wires are twisted together and are exposed to the same noise signals, so basically the noise cancels out. The idea behind BNC is to have a small wire carrying a sensitive signal in the center and have that surrounded by a tube of wire, that acts as a shield for the inner wire and is normally connected to the circuit ground. But since a thermocouple has no circuit ground and neither does the multimeter... I think twisted pair is simpler and easier to deal with.
Atmospheric changes, I have no idea. Depends on the unit. If it's not specified in the manual, don't worry unless you have extreme conditions out there. (make sure you can get the manual on PDF. For Keithley and HP you can get the PDF manuals online, but you have to give them your name and email, which is not that bad). What really does affect them can be very high humidity.
There is no field calibration routine for the multimeters themselves, apart from nulling. Maybe for your aplication there could be, like reading the voltage of your sensor at room themperature, but that depends on your application.
One thing to keep in mind. The input impedance of these multimeters is typically more than 1 gigaohm for 2V and 200mV ranges only. That is a really high impedance. You can read voltages directly from thermocouples with that. Apart from that, the input impedance is 10 megaohm for all other ranges. Lead resistance will do nothing for voltage measurements at this impedance. Noise is the problem here. That is why i suggested BNC cables earlier, because there is a shield. Either BNC, with the negative shield grounded or twisted pair cables.
Moving on to a completely different topic.
Buying a used multimeter. Get one that doesn't look physically abused, if it has a calibration sticker on it, with a recent date, even better. That means someone was using it and took basic care for it and that it didn't sit on a wet basement corner.
Now, technically speaking, you'll never know if an eBay multimeter is still within its accuracy specifications (within spec.), but practically speaking, these multimeter after some time, don't drift very much from their specifications, after some years they settle. So you either get a multimeter that's accurate, or you get something completely out of place.
If you absolutely need to know if the thing is accurate you have a couple of options:
*Send it to a calibration lab for calibration only (no adjustment). Calibration is when they check whether it meets its specifications or not. Adjustment is when they tweak it so that it meets its specifications.
*Or you can buy a little home lab voltge standard like this one:
http://www.voltagestandard.com/-.htmlThere are some voltage standards on that page.
Me? Meh, I haven't calibrated mine or anything. The day I meet someone with a multimeter as accurate as mine I will invite him or her to compare the measurements to see if both multimeters agree.
You don't need particularilly expensive leads for this multimeter, but since your aplication involves thermocouples, I don't really know what effect my suggestions will have on your measurements.
For normal multimeter probes, you can solve the problem in several ways, many of them are discussed in the post I linked in my previous message.
For thermocouples, I don't know enough about that, bud Dave has some good videos, I did like them. Here's a thermocouple tutorial:
And I think he talked about thermocouples in one of his very early episodes (50-smonething or something like that)
I hope you find a 5 and 1/2 digit multimeter for cheap, and that it wourks out for your project and for other tasks you might find later on. They're handy.
-Ivan
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