A pointing machine is a framework of metal arms which can be fitted around a sculpture to measure the relationship between given points on its surface. The apparatus permits these measurements to be transferred from the sculpture to another mass of material, such as a block of stone, thereby copying the original sculpture in correct proportion. Greek and Roman sculptors are known to have used pointing machines, and they were re-invented during the Renaissance. Further improvements were made in the 18th and 19th centuries, including machines that allowed small models to be scaled up. Video here.