A DIY shutter speed tester.
Shutter and iris are the main functions of older cameras that can have suffered over time. Build-up of “muck” or sticky lubricants getting where they shouldn’t mostly are to blame but a well cared for and gently used camera can have worn well. Those that have suffered may still have shutters that work fairly well, just a bit erratically whilst apertures and focus may be a little stiff but will still be accurate.
If the shutter isn’t bad enough to warrant laying out for a full CLA (clean, lubricate and adjust), a means of checking what actual speeds are being delivered is useful to ensure good exposure. Film latitude is quite forgiving and digital editing is extremely accommodating, but there is no substitute for getting the result you want from film, monochrome or colour, by having control of exposure.