1. Roads were originally conceived as coloured markings on the bubble chamber negative. In the development of ideas for a convenient and workable system,L. Kowarski first introduced the idea of a separate carrier for the roads. Alternatives to our present choice exist in which the road carrier is scanned by an auxiliary spot. While these enable the road carrier to be different in size from the original photograph the present system seems easier to construct and to use.
2. The possibility of transmitting additional « ordering » information from the measuring machine to the computer to simplify programming for track recognition has been emphasized byY. Goldschmidt-Clermont and his particular suggestions are incorporated in our present design.