To try and answer my own question about the uncertainty on the Fluke 87V uA range I went on the official Fluke website and downloaded various docs about this meter. In the User Manual the spec for uA on the lower range is given for the standard setting (not 4 1/2 digits)
This is +/-0.2% and 4LSDs. So this implies +/-0.2% with 0.4uA uncertainty if the LSD is 0.1uA. I don't see how changing the resolution can improve this uncertainty and I read the specs from start to finish and found this on another page:
Quote:
Detailed Specifications
For all detailed specifications:
Accuracy is given as ±([% of reading] + [number of least significant digits]) at 18° C to 28° C, with relative humidity up to
90 %, for a period of one year after calibration.
For Model 87 in the 4 ½-digit mode, multiply the number of least significant digits (counts) by 10.
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So does this make sense? You still end up with 0.4uA LSD uncertainty even on the 4 1/2 digit range because 0.01 x 40LSD = 0.4uA? Have I read this correctly?
So it would appear unwise to attempt to use this meter on the uA mode if your target spec was 37.5uA +/- 0.1uA. The accuracy for DC current is already degraded to +/- 0.2% but then there is 0.4uA of LSD uncertainty on top of this.
So even if you had it calibrated you can't escape the uncertainty limitations and it doesn't seem wise to use this meter on this DC uA function setting (for the 37.5uA +/- 0.1uA requirement) even with a freshly calibrated meter straight out of the box from Fluke. It would be much better to use the other method with a precision resistor and a cheapo 0.05% voltage reference to add confidence to the measurement?