On a fixed schedule prior to the shot, the timing mechanism in the control room back in Yucca Pass sets in motion the whole mechanism at the tower, on the ground, and in block houses and © bunkers in the area. Frequently the most useful measurements are ‘those of what takes place within the detonation itself, Since the measurements must be made in millionths of seconds -- or less-~- the resolving time of equipment must be incredibly short. To catch the imme- -diate early phenomena of the detonation, the detectors and gauges must be placed on the tower in close proximity to the unit being tested, This,.of course, means that the detectors are almost in- stantly vaporized, but in the millionths of a second before they are destroyed, they transmit the all-important signal to the recording devices in the bunker, Instrumentation in the bunker consists mostly of power sup- plies, amplifiers, oscilloscopes, cameras, and other recording devices. Large coaxial cables carry the signal to the recording machines from the gauges and indicators outside. The electronic recording circuits respond extremely rapidly. They can be made t® operate in a few hundred-millionths (0.00000001)seconds. A great deal of light is required to write on photographic film in such a limited time. Unless special precautions are taken, this light would badly fog the film during the many minutes the instrument is waiting for its signal to be given. To solve this dilemma the electron beam is reduced in intensity and deflected off the screen prior to zero time. At the last possible instant it is necessary to raise this intensity to its required value. By an ingenious arrangement, the coaxial cable is tapped so that the signal itself can trigger an intensifier. The signal, however, passes through a greater length of cable and hence appears at the scope to be recorded a micro-second or so after the intensity has been increased, The record is of very short duration, Fortunately, however, the fluorescent oscilloscope screen retains the image briefly after the electron beam has swept across. The persistence of the image, analagous to a modern television tube where no flicker is dis-~ cernible to the eye, is sufficient to permit permanent recording on the photo film. : Thes@> films are the raw data from which the results of the experiment are interpreted. After the shot, re-entry to the building and recovery of the data is made as soon as radiological safety precautions permit. This is normally within a few hours after the blast. Sort tna” t ce . - 35 - . -&