Stroboscopic disk sets wrong speed for turntable?

Wow you guys are good. Can you figure out my copy of Kind of Blue? Side 1 seems a little off....
https://forums.stevehoffman.tv/threads/miles-davis-kind-of-blue-mono-speed-issues.232772/

It is for the first 3 tunes where one of the tape machines ran slow. As the playback for mastering was on a different machine, these tunes are sharp on the early lps.
This was corrected later and is explained on the columbia legacy jazz cd that I have,

I read sometime last year that the regulatory agency for the utility companies relaxed the standard for 60 Hz, because it was too expensive and time consuming for the utilities.  So some type of device/app is now needed, that is not dependent on power company frequency.

bgpowell

I read sometime last year that the regulatory agency for the utility companies relaxed the standard for 60 Hz, because it was too expensive ...

I think your memory is failing you. First, there is no single regulatory agency for power distribution. Rather, regulation is left to individual states.

In the US, there are numerous distinct electric power distribution grids and they are managed by the non-profit NERC. It ensures reliability and sets the standards power suppliers must observe. Among them is power line frequency.

Power line frequency is tightly controlled within each regional grid. That is because each regional grid is supplied with power from multiple energy providers and all of that power must be properly synchronized (within tolerance) for the system to be reliable. The actual voltage provided by individual suppliers has a fairly wide tolerance - but not so the frequency.

The stability of the each regional grid hinges in large part on that tight synchronization of power, which is typically around ± .5 hZ. If imbalance between load and demand causes a substantial frequency deviation, automatic relays will shed load to preserve the frequency and the stability of the remainder of the system.

Of course, that may not be a tight enough spec for audiophiles using a synchronous motor on their turntables. For them, there are products such as the VPI SDS or ADS, and other products such as PS Audio’s regenerators.

I agree with Lewm that the battery powered KAB strobe would be the best way to go.
When I purchased his Walker motor controller for my Nottingham TT I first used a generic disc and a AC powered bulb to set speed.

Then a friend loaned me his KAB strobe and lo and behold it showed the AC setup was slightly slow.

Not cheap but highly recommended!