I have one K1000 body which I do not use now because of another issue, but the meter has always been accurate from what I can tell. I've been told that the K1000 (and other Pentaxi of that era) are relatively insensitive to slight battery voltage variation, compared to many others.
I've been kind of vocal off and on about being frustrated by meter accuracy, or more correctly not knowing if they are correct. I just find it so mindboggling that we have means to measure just about any quantity of anything there is (volume, mass, length, etc.) with very close precision and accuracy, but not light! Calibrated light sources are well beyond my budget!
The best I've been able to do is a sanity check under sunny-16 conditions. My back yard (looking into a wooded area out the back door) in early afternoon sunlight is very close to sunny-16 on all of my cameras. If I suspect that metering is off, that's what I check for. They tell me (the ubuquitous "they") that afternoon sunlight with a clear sky is very consistently just over 100,000 lux.
In fact, it was not that long ago that I answered a thread about using the "wrong" battery in a Canon GIII on another board and I did a quick comparison between the GIII that I have (with the "wrong" battery) and the Pentax MX and found them less than 1/2 stop in disagreement.
I would sure love to have a cheap and convenient "lab standard" light but those apparently don't exist, other than the sun. A 50 cent ruler is accurate within a percent or so. A $1.99 set of measuring spoons has to be within a few percent at most. The bathroom scale is too accurate!
How about light?