The most important tool that I used at English Heritage was a ‘pointing machine’. This instrument of brass tubes with beautifully machined joints is used for making a precise copy: three fixed points are chosen on the original and corresponding points are carefully located in the block from which the copy is to be made. It works best if the down-turned top point allows the machine to hang from the job. The movable arm with an articulated sliding depth-stop is used to transfer a series of points from the original to the copy, withdrawing the pointer while stone is cut away until it slides home against the stop. For very large copying the machine can be set up on the original in several locations to cover the entire surface.