Radius gauges require a bright light behind the object to be measured. The gauge is placed against the edge to be checked and any light leakage between the Plates and edge indicates a mismatch that requires correction.
It is a kind of observational measurement because of its visual test way.
R1-7mm includes 17pcs at each end, radius as 1mm, 1.25mm, 1.5mm, 1.75mm, 2mm, 2.25mm, 2.5mm, 2.75mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm.