Low-cost frequency meters
I have a Kill-A-Watt P3 which always shows 59.9 Hz as the frequency at my home. One of the digital LCD meters sold on eBay bounces between 60.4 and 60.5. For electric clocks with synchronous motors ( the old dial type), 59.9 Hz would result in a loss of 2.4 minutes per day. 60.4 Hz would result in a gain of 9.6 minutes per day. My atomic clock and the old electric stay quite close, so these meters are just not accurate.
The power companies place great emphasis on keeping the frequency at 60Hz. As far as I know, all the major power companies in the USA are synchronized in order that power can be shared or transferred at will.
Have you gotten readings on some meter that vary from the expected 60Hz?