TT motor variable speed or digital tachometers not precise?

Have anybody check their TT motor or platter speed with digital Chinese made tachometers sold on Ebay? If yes what are the results. Mine shows motor speed varies up and down from 369 to 375 on three different motors. So, i'm wondering is it tachometer fault or motors?
There are several threads that address this issue.  In general I would not rely to heavily on an inexpensive chinese digital product in terms of either accuracy or precision.