The HiQ is dedicated for use if a monitor chamber is required, and the midrange 617 is used for collecting charge on the Attix chamber....
I went to through the second document and it was interesting. They only really highlight doing calibration on the 617 using a 1nF capacitor. But they do list the values of their NIST calibrated capacitors, their highest being 100nF. I'm assuming this is the capacitor they use to verify the 617-HIQ.
Based on other calibration procedures for the 617, Keithley usually don't use the lowest range for the calibration procedure, but one of the mid-ranges. For the 617, you would calibrate on the 2nC range so the use of a 1nF capacitor makes sense. For the 617-HIQ the mid-range is 2uC. I would venture a guess that you would normally calibrate using a 1uF capacitor. Although, in that document they don't mention having one, so unsure which value is correct.
Digikey has, 100nF 1% Mica capacitor for ~$20 (honestly more than I care to spend)
Mouser has some 1uF 1% Film capacitors around ~$3
Both have 1% tolerance Film/Ceramic 100nF that aren't too expensive.
I'm pretty much finished with my shielded test fixture, although I still need to work on the inner box for using guarded measurements. Also need to make some more leads to connect everything.
So far the 2450 is telling me my 100G resistor is: 100.0937G
So with the calibration current of 190pA, I'm looking at a test voltage of: ~19.0178V
Hopefully I will get to go through all the steps on Sunday. Sounding like the wife has some plans for me tomorrow...and still need to do some additional work on my test fixture.
The 617 didn't seem to appreciate me waving around a heat gun for hours melting PTFE heat shrink. It still hasn't calmed back down to the normal ~1-5fA yet. Hopefully it will stabilize in a few more hours.