"John A" wrote in news:4666bbdc$1$8756$ed2619ec@ptn-
nntp-reader02.plus.net:

Well, I intentionally didn't suggest adding a variable as a) it would
re-open the Pandora's Box of how to calibrate the thing, and, b) the
combined tolerances of the fixed components would make a nonsense of such
calibration anyway.


Another thing: That variable cap on the page David (and I) linked to, is
more than 1 nF. So long as the fixed caps had a tolerance tight enough, it
should cover (1.398 nF allows for greater than 20% tolerance on nominal 1
nF increments). Not that any of this matters, in practise.