Years ago electron microscopes usually had an hour meter as a standard part of the instrument Unfortunately hour meters have been eliminated from many modern scapes and are not even readily available as an option from most microscope manufacturers.

An hour meter is a very useful device. Every microscope I've owned or supervised has had an hour meter that was factory installed, added by helpful field service persons, or that I installed myself. Few of us would enthusiastically buy a car without an odometer, why should we want an electron microscope without an hour meter?

If supplying an hour meter on an electron microscope costs too much in production time or money, certainly it would take only minimal effort at the design stage to plan a connection point or plug to operate a clock as an ancillary part of an appropriate circuit.