The Enlarger-Projector described was designed to facilitate the measurement and comparison of four C.R.O. traces obtained simultaneously on a transparent film. The traces represented pressures attained during gaseous explosions in compartmented structures; the phenomenon known as “pressure piling” caused high and local transient pressures. In the instrument described the operator has a magnified view of each portion of the record displayed at a normal viewing distance from his eyes, and the view may be shared by at least one other person. Measurements of adequate accuracy can be made rapidly and conveniently.