I have made my living for 25 years installing and repairing industrial scales . A mechanical scale will hold it calibration for ever as long you dont loose anything and it does not bind and is correctly zeroed at the beginning , The beam should float freely up and down a few times before stopping and it should repeat the same reading with a given item every time . A check weight of a known value is a good idea on something as important as reloading . Electronic scales are much faster , should repeat and NEED to be checked every session with a calibrated test weight . about 2 years ago i bought a cheap RCBS electronic for my reloading and have a old Lyman as a backup that Has served me well for many years .
The mechanical will still work for many years after the elctronic has died , I would guess the electronic scale will last 5 years on average