Gates 91132 Belt Tension Tester

I initially bought this belt tension gauge for my 1990 ford ranger.
It took me a few minutes to understand how to use it since the instructions were not crystal clear.
Honestly it proved ineffective to test my serpentine belt, because the gauge always seemed to indicate that the belt was loose, but all the components driven by the belt were actually working fine (alternator, power steering, water pump etc); no slippage, no squealing, no discharge battery as a result of loose belt on alternator pulley, etc.
The reason I still give three starts to this product is because I give it the benefit of the doubt: I probably didn't use it properly. I guess I did something wrong which is why I had a low tension reading. Also, it is only $25 which is not bad for a belt tension gauge, and it is small and will fit in any toolbox.