On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:

I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.


They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.