HP 53132A accuracy question

[bristpi176]

Hi all,

I'm testing a recent purchase, an HP 53132A with the 3GHz option and an aftermarket OXCO.  It passes all its self tests and passes calibration. After a couple of days warm up, I had it count its own reference with small variations of the least significant digit (400 microhertz), so I consider that good. 

The question is, when I calibrate it against my house reference, an HP 58503B that appears to be working well, it shows 10MHz, with variation in the least significant digit varying, then the count drifts lower over time and seems to settle approximately 50 millihertz down while still on the house reference.  This process happens after every calibration.  Does this sound like normal output?  If not, what do I do to get it to read properly.

Thanks in advance for any help you can provide.

[coromonadalix]

you have aging effects to take into consideration for your aftermarket board, and your home instrument reference,  does it have ocxo  tcxo  in it ??

do you have access to an gps do ?

[bristpi176]

My house reference is an HP GPSDO.  As far as aging, I'll continue to run this experiment until I see several days of consistent output.  It still may be dropping but more slowly