[time-nuts] SRS SR620 External Source Issue -- Help Request

[TheInfamousFlavio at hotmail.com]

I have an SR620 counter that I set up with a Z3801A as an external reference.  If I put a bnc T connector at the output of the Z3801A and use two equal length bnc cables, one to the ext. ref input on the back and the other to channel A then do a frequency measurement, I get a mean that is about .0015 Hz below 10,000,000.0000Hz.

Does any know why this might be happening? I would expect it to read 10,000,000.0000 exactly give or take a couple on the last digit.