When deciding the best way to measure a component on a co-ordinate measuring machine (CMM), many choices are made by default because they have been carefully thought through many times before. The accuracy specification of the CMM, the best type of sensor to use (touch or scanning) and the optimum probing method are often taken for granted and not questioned. However, this foundation for good metrology can be undermined by an inappropriate or ill-considered choice of stylus, with the result that measurement accuracy can be compromised.