Aux belt tension

[Cupman29]

Fitted a new aux belt this afternoon and thought I'd check the tension using my new Renault tension meter. The manual says it should be 183Hz but I can't get it over 150Hz and that is seriously horsing it up to the point it feels like the belt is about to snap (probably not but it's tight anyway).

Does anyone else use this meter and get it to 183Hz?

Cheers