Looking for a specification of the HP 11953A termination resistor (BNC).
Measurements of two different units indicate R=51,3 Ohms.
I would have expected something closer to 50 Ohm.

Yes, the ohmmeter is calibrated...

=====================
What is the uncertainty of your ohm meter ? If it is a DVM then apart
from the uncertainty the actual value is plus/minus 1 of the least
significant digit.
You really have to define 'Ohm meter is calibrated'

Frank KN6WH / GM0CSZ (currently in California)