Catra has own sharpness tester and many other useful products for edge testing. Catra uses rubber or silicon rubber test media. Typical Catra sharpness of a razor blade is some 30 to 40 gf.
http://www.catra.org/pages/products/kniveslevel1/st.htm
Jan
P.S.: My Lego education sharpness tester used rubber ring also.
http://www.catra.org/pages/products/kniveslevel1/st.htm
Jan
P.S.: My Lego education sharpness tester used rubber ring also.

