Hi Dave,

I don't recognize, which problem you wanted to examine...

The 50 Ohm range had two different probs, than simply being in/out of spec.

First, if you apply F.S. of 50 Ohm, you may encounter an unstable reading on the last two digits, although it should be stable at this high test current, and also compared to the ranges of 500 Ohm to 500 kOhm. Even the 5M Ohm is stable to the last digit with FW 1-26.

Also, it's a bit tricky to make a correct REL setting, when shorting its input.

The 50 Ohm range resolves 1mOhm, which is a great favor of your 121GW. Clearly, you need to use REL to zero any cable resistance, so afterwards to measure precisely resistance in the Ohm range, with 1mOhm resolution, and even accuracy.

I was disappointed though, because the calibration of UEI had introduced a threshold, by too high residual zero calibration, which also seemed to affect this described low ohm measurement.

**[EDIT:]**

*So if you short the 121GW with successively lower resistance from your resistor box with 10 mOhm resolution, you can check, when this obvious threshold steps in.. maybe at about 100..200mOhm, which might suddenly give a straight reading of 0.000 Ohm.*

Anyhow, I have improved the zero calibration by using a massive short, and then the gain by a precise 50.000 Ohm reference.

After that procedure, I really can use the 121GW to precisely measure resistance in the mOhm range, either correctly zeroing cables, or determine residual resistance of my resistor box, or making measurements of 10.000... 50.000 Ohm resistors, much better than the spec.

That 1 mOhm resolution feature is a great plus of the 121GW, so I would recommend to make an effort on proper calibration.

Frank