The hypothesis of the existence of the megalithic inch, proposed by Thom, has been tested on cup and ring carvings in West Yorkshire. An apparent quantum emerges that is very close to the value proposed by Thom, and this is supported by evidence from cup spacing, as well as ring diameters. Cups with surrounding rings appear to be closely related to the measurements made by the prehistoric carvers, and there is evidence for the use of five megalithic inches as a basic unit. -- AATA