We gain precision from more fun with Ohm's law

I did try the microammeter from the previous blog:

https://wb9kzy.blogspot.com/2025/04/nanoammeter.html

and it does work, giving 2 more digits of precision to current readings - more digits not necessarily more accuracy :)

The quiescent current used by my two fave LDO regulators, the S812C50 which I usually measure as 1 uA with the Metex ME-11 in the 4 mA position measures as 0.58 uA with the following circuit:

So the Metex is rounding up to 1 uA from .58 uA - seems reasonable.  With the LM2936 I usually measure 7 uA with the Metex, now it measures 7.31 uA using this new technique.  So in that case the Metex is rounding down the reading.

What is the error from putting the two resistances in parallel ?  Very tiny, I work the equivalent resistance out as 9990 ohms which is 99.9 % of 10,000.

(10k x 10 meg) / (10k + 10 meg) = 9990 ohms

A 10 k ohm, 1 percent resistor is pretty cheap compared to a 5 1/2 digit DVM !

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm