I was using my Pentax digital spot meter yesterday and got to thinking about the fact that I've never had it calibrated or even tuned up in over twenty five years and thus have no way of knowing if it is accurate. Let's say, for the sake of argument, that it is many stops off of some absolute standard and that what it reads as EV 12 is really EV 9. Since I use the same meter for all my exposures and have determined my own exposure indexes and development times for various films based on this meter's readings, what good would getting it calibrated do? It seems to me that as long as the meter is able to read relative values accurately--a six stop scene brightness range meters as a six stop scene brightness range--then all is good.

So I was wondering: is calibration of photographic measuring devices important, or is it better to use consistently functioning equipment in the same manner every time?

Jonathan