Let me begin my description of how we have been doing computerized microphotometry with a brief history of the hardware and its evolution. Then I’ll get on to the more interesting topic of what we do with the data after we get them into the computer.

In 1966, the Shock Tube Laboratory at Harvard College Observatory took delivery of a David Mann microphotometer. Briefly, this $50 000 instrument can measure positions in an area 250 x 250 mm to an accuracy of about 1 μn. The limiting resolution of the measuring slit approaches 1 or 2 μm at the plate, and the drift in the photometer output is on the order of 1 per cent in 12 hours.