i seen a post from a few years ago about some one had a motor running low and that they tried to adjust the speed and nothing happened .. said something about being below 50hz ...
that reminded me that i have a kill-o-wat meter and it does show hz ... though im not sure if its a counter .. or switches 50/60 when its close ...
i sapose if it only has 50 or 60 that when it switches showing from 50 to 60 that it would be fairly close for most anything ...