The early history of the HPD

Abstract The initial stages of the development of a system for the rapid measurement of bubble chamber photographs are described. At first called the IEP-X and then IEP-Y, the device which came to be known as the HPD was adopted by several groups both in Europe and the USA. Based on a mechanically generated flying spot, it was the first machine to use this technique for bubble chamber film measurement. Operated in the “road guidance” mode, it provided considerable measurement capacity combined with excellent precision and very acceptable bubble density measurements.