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shot and of being damaged to some extent (loosened threads, packing washers). 
A less troublesome system is simply to use a piezoelectric gauge of suffi- 
ciently rugged and waterproof construction, Such a gauge develops a repro- 
ducible signal, is easily tested, and unless damaged requires no maintenance. 
It can be placed at almost any desired position in relation to the charge and 
other equipment, thus providing considerable freedom in timing without need 
of auxiliary delay circuits. 
For some experiments, it is desirable to fire one or more detonator 
caps with a minimum time delay. A condenser discharge circuit can be used 
to fire two or more caps in series with short delay and a difference in 
firing times of 5 to 10 psec. 
