Picoammeter measurements and special test leads

[Kiriakos GR]

If it happens of you to own:
Tektronix DMM4050 and or
Fluke 8846A and or
Keithley 6485 ..

In case that you are interested to measure down to pico ammeter range.
DMM4050 / Fluke 8846A, both DMM at their lower 100uA range they can deliver 100pA at their last digit (max resolution).

Keithley 5 1/2 digits 6485 Picoammeter this has more ranges lower than 200uA,
20uA , 2uA .
200nA , 20nA ,2nA .

Apples to apples comparison 8846A this is superior to Keithley 6485 Picoammeter due it 100uA range VS 200uA of Keithley.
8846A due it far better resolution of 6 1/2 digits, it can even compete at measurements down to 20uA  or lower.

What I was not aware so far, this is that Keithley this suggests special test leads for their Picoammeter,  and those test leads they are made with:
a) BNC plug
b) 110 centimeter RG58C/U
c) 10 centimeter black/red wires, them terminated to alligator clips.


I am now challenged to discover at which lower current measurement value, the coaxial RG58 this will make the difference against my own 2.5mm clear copper pair of test cables which they are the finest test cables sold in Europe.
Keithley 6485 Picoammeter datasheet it does mention maximum input capacitance 20nF for 200nA , 20nA ,2nA ranges.
And 1mF for 20uA and above ranges.

 
I do find Keithley datasheet this be somewhat misleading, one meter long RG58 this has almost 100nF of capacitance.

How to make your own capacitor for 100nF multimeter range testing
https://www.ittsb.eu/forum/index.php?topic=1442.0