Seems to be. The test resistors are big long blue things from Digikey, IRC maybe. I have a set of resistors from 1K to 5G ohms, each mounted on a Pomona dual banana plug.
I'm using two DVMs, one to measure the upper (Z1) voltage and one across the lower (Z2). I can short either pair of terminals and zero out the respective DVM. If I plug in 1G and 5G resistors and apply a few volts, I get a voltage ratio of 5.002. A good diode makes a nice log curve down to 20 fA, which is comforting.
Being a little paranoid, I've done a number of cross-checks and everything looks good so far.
I do have some surface-mount 100G and 1T resistors; maybe I'll ratio them just for fun.
My ebay Keithley electrometer just arrived and seems to work. The lowest range (on the analog meter) is 1e-14 amps full scale. It measures the 1G and 5G resistors within a couple per cent. Looks like this:
John