724 
The sweep speed was calibrated by placing the output of the time stand- 
ard described in paragraph (vi) on the vertical plate of the cathode-ray 
tube; this calibration was done immediately before the shot was recorded in 
order to minimize any possible drift in sweep speeds. 
The most reliable method for tripping the sweep was by the use of a - 
pilot gauge at some point between the recording gauge and the charge. The 
signal resulting as the shock wave struck the pilot gauge actuated both the 
sweep and beam brightener, The distance between the pilot gauge and record~ 
ing gauge determined the time interval between the beginning of the trace 
and the peak of the pressure-time curve. 
(ix) Time delay. For recording several phenomena which occur within 
a few milliseconds of each other, only one sweep circuit necd be used, the 
X-axis positioning control being adequate to cause the record of the desired 
phenomena to occur at the proper position on the cathode-ray tube sercen. 
However, if these phenomena occur at times differing by more than a few 
milliseconds, more than one sweep must be useds Such a situation exists when 
gauges are used for recording the shock wave at several distances from an 
explosion. As additional pilot gauges for tripping thé additional swceps 
would require additional cables for transmitting the tripping pulse back to 
the vessel, it is more convenient to use a circuit capable of producing 
pulses for tripping the later sweeps at fixed time intervals after receiv- 
ing the pulse from the trip gauge, A time delay circuit which would give 
one pulse with zero time delay, and two other independent pulses at any de- 
sired time from 0 to 100_msec after the trip pulse input was uscd routinely 
with still~film cameras on the RELIANCE. The two gauge pairs at the two 
closest gauge positions all operated on a sweep tripped at zero delay, the 
third gauge pair on a second sweep tripped by the first time delay, and the 
fourth gauge pair on a third sweep tripped by the second time delay. 
(x) Rotating-drum cameras. Camera backs fitted with rotating drums 
of 10.0-in. circumference were alsc used on the regular camera tubes mounted 
on the oscillographs (Fig. 17), For the eight channels on the RELIANCE 
these cameras were driven by means of flexible shafts from a conmon drive 
shaft. Also driven from this common drive shaft were the synchronizing 
control cams and tachometer in the sequence beam brightener panel, These 
synchronizing cams fired the charge at a timc so that the record would not 
come on the break in the film, brightened the cathode-ray beams at the be- 
ginning of the revolution and shut them off at the cnd, and also caused 
the crater tubes to flash for one revolution. These crater tubes are driven 
by the multivibrator described above. 
Among the advantages of the rotating-drum camera for this work are the 
following: (1) the time calibration can be recorded simultaneously with ~ 
the pressure-time curve; (2) there is no difficulty in reading the records 
due to nonlincarity of sweep speeds; (3) it is not necessary to use a trip 
gauge or other device near the charge to brighten the beam for recording, 
since this is done by control cams; (1) non-orthogonality of the cathode- 
ray tube plates need not be considered; (5) a large range of recording 
speeds is casily obtained and by means of the tachometer the approximate 
