Lena Zavaroni behide the clap-o-meter
Quite often a clap-o-meter is a complete sham, having no real sound measuring equipment at all.
It is, instead, manipulated by a person, based on their estimation of the audience reaction.
This is normally done semi-openly, with the audience under little or no illusion that the clap-o-meter is genuine.
This was apparently the case on Opportunity Knocks, where the clap-o-meter was not used to actually determine the winners and was disclaimed with the phrase "Remember, folks! The clap-o-meter is just for fun!".