I use a Boonton 76-3A precision decade capacitor for my calibration checks. I originally picked it up for calibration of an old Boonton 72BD meter (0.001 to 2000 pF capacitance range) but it now also serves as a good calibration check on a few HP units that I have. It has capacitance selection from 1 to 1221 pF in 1-2-3-5 x1, x10 & x100 ranges. Accuracy is 0.1% ±0.001 pF. The connections are made through special BNC(M) connectors without outer bayonet shell. But the unit can occasionally can be found in used condition with the Boonton output connector adapter to normal BNC(F) interface or you can make your own.
They sometimes come up pretty inexpensive on ePay amidst the real price gougers.
Greg
