M830B voltage differs with polarity

[hapless]

I've been searching/researching and scratching my head for a while, but couldn't come up with an answer to this.

I got an M-830B as part of a tool set. The meter looks exactly as on P. Vis's page inside, the only difference being that mine is black. I've looked at schematics floating around the 'net and they don't seem to match the PCB.

The problem that I've encountered is that the meter should (and I know that these meters can) show the same voltage regardless of polarity. However, the one I have is a few counts off when polarity is reversed. E.g., it would display 5.00V, and then reversing the probes would show -4.98V. Not a big deal for such a cheap meter, of course, but I'm sure there's a way to balance this out. Any suggestions would be welcome, and also, maybe a place to find the correct schematic.

[Vgkid]

On a bench(The only ones that really go into detail describing this) meter it would be due to a asymetrical difference in the analog to digital converter. It is present on my meters.

[hapless]

Thanks for the reply. Hmm... If that's the case, I'm out of luck. I kind of hoped it would be something like the fault of a ceramic cap in auto-zeroing circuit having too much V loss or something like that.

[MK]

If it is only 2 Least significant digits, then you just have to live with it or become a volt nut who aspires to an HP 3578A eventually...
 

[Vgkid]

With only 2lsd, not much to worry about. My 87-1 agrees to the same digit in 3.5 digit mode...

[hapless]

Interestingly, without the tiny shield on the cover connected, it can be as much as 5 lsd. As you probably can tell, I'm not too worried about it as it's not the best meter that I have. It's just something that would be nice to be able to correct. The issue came up when I started adjusting the only pot on the PCB against a precision voltage reference. I guess adjusting for the positive polarity is the best I can do then. Or would it be better to adjust for the negative just in case most of my future measurements will be done with probes reversed, as per Murphy's Law they usually are?  Current measurement is also affected by the adjustment, but it would be way off in either case. The shunt resistance just has to be figured into the measurement results.