The other day I bought a cheap plastic 150mm/6In digital calliper for 8,00 with the intention to mount it on my Optimum F45 mill as a Z axis gauge. It has a total course of 120mm and it looked just right for the job. It was the first calliper I saw that works in mm, inches (decimal) and inches (fractions) Sorry about the picture quality as the mobile phone's camera and poor lighting conditions don't mix well.