Harley Benton Understring Radius Gauge

I bought this gauge to be able to get the same radius to the bridge/saddles on my strat type guitars as the fingerboard radius. For that it works. However the markings for the radius isn´t correct. I tryed it on several guitars that have 12" radius fretboards and the gauges showed 10". Aslo the edges are almost razorblade sharp. I can live with the sharp edges on a cheap product like this but it should show the right radius. Therefore I give it a low score.