[Amps] how to measure impedance - 8405a vs 8415

[Dan Sawyer]

All,

I would like to measure impedance. Does anyone have direct experience 
with using either an 8405a or an 8415 to do this? If so what are the 
relative merits of each?

A second question: I have an 8505a that appears to be close to working. 
When attempting to take a reading the meters seem to move continuously. 
Sometime this is obviously wrong and it oscillates from min to max. 
However sometimes it could be 'ok' and the oscilation  is 10% or so of 
full scale. Is this normal??

Thanks in advance,
Dan