The paper tape recording was driven directly by the wheels of the locomotive, with the paper spool moving at a fixed rate per kilometre travelled. Two graphs were recorded, the first being time elapsed (with the trace moving vertically if the train was stationary), the second being a speed curve.
Read together, it was possible to determine exactly what speed the locomotive had been travelling at any point in time or distance. As well as allowing study of locomotive performance, it also allowed greater scrutiny of the observance of the driver of speed restrictions along the line. It was practice on some railways such as the Victorian Railways in Australia for the driver to sign the speed chart prior to departure.