[time-nuts] Old Crystal.

[ed breya]

I didn't realize before that there was a picture attached in the OP. 
That's a lot different from the HP ones. The crystal element looks more 
like those in regular packages, but on the large side, due to the low 
frequency. If it's a 1 MHz, then you should be able to find plenty of 
representative example oscillator circuits around that frequency. It may 
be just a regular type, not for an OCXO application, but fancy glass 
packaged because of its size.

Ed