VINTAGE International Crystal C-12M Frequency Meter

Found along with some other items while cleaning out father's estate - he was a service tech for many years - don't know anything about this so if anything need me to check, etc. let me know

One of the contacts on one of the 9v battery connectors is broken off (see pix) - the clear acetate cover that fits inside the top cover over the calibration service record is discolored and should be replace