These signals are used, in the photo station, to open the rolling door of the cab, to apply power to electronic equipment, and finally to start the cam- eras themselves. Each signal is sent ata definite time relative to the FIRE signal to the bomb; the several signals are precise to something like +0.05 seconds. The sequence of signals used in the photo tower is: - 15 minutes: Apply filament power to electronic equipment - 1 minute: Open cab door - 15 seconds: Apply plate power to electronics - 1.5 seconds: Apply power to Eastman camera motors 0 seconds: + 1 second: Test signal (for dry runs only) Remove power and deactivate station. The photography for determination of yield is a prime measurement; . failure of the photo station in any respect is considered grounds for postponing the shot. Consequently an interlock switch, activated by the photo station, will be inserted in the FIRE line, and the bomb will not be fired unless; a) the cab door is open, b) the film-speed mackers are pulsing, and c) power is applied to the camera motors. . To maximize the reliability of station operation, the installation will be operated as if it were two separate, independent stations. timing signals will be supplied from the control room. Two sets of Each signal set will operate three Eastman cameras and independent electrical circuits. Each of the two "camerastations" will provide an interlock signal, and the two interlock switches will be connected in parallel. As will be seen, four of the six cameras are to be operated for the U. N. program; the other two are for AEC purposes. To assure proper operation at shot time, it will be necessary to have a simulated dry run, which will duplicate as nearly as possible the intended operation at shot time. For the dry run the station will be set up and checked out, exactly as planned for the shot itself. Operators and Obser- vers will stand within the cab to see that everything works properly, but they will not be permitted to throw switches or to interfere in any way with the automatic working of the station. The films will be developed at Parry, and will be inspected to see that the film-speed marks are of adequate - 25 -