Gauging the speed of the turntable at 78 rpm is a tricky procedure, but it has to be right otherwise the pitch of the recording will be wrong. Until recently the speed could be adjusted using a strobe disc that fitted onto the turntable. Under standard electric light which oscillated at 50 times per second (without our being aware of it!) a series of lines on the strobe disc appeared stationary when the correct speed was reached. With modern LED lighting, however, I am not sure whether this would work? In the 1920s/30s HMV, and others, produced patent devices that indicated when the correct speed was reached. These accessories are now collectors items as well as being practical aids.