This device measured acceleration by means of a gyroscope, which was mounted in such a way as to act as a pendulum. The resulting mechanism performed a mechanical integration of the measurement of acceleration, which by Netwon's calculus gives the velocity. Because the gyroscope acted as a pendulum, and because the properties of the gyroscope gave the mathematical inegration of acceleration, it was called a "PIGA," for "pendulous Integrating Gyro Acclerometer." The "25" referred to the diameter of the housing for the gyroscope rotor, 2.5 inches (about 6.3 centimeters).
Among the several ballistic missiles and spacecraft that used these devices was the Titan II Intercontinental Ballistic Missile, which was also used to launch m,anned and unmanned Gemini space capsules.
The MIT Instrumentation laboratory, of Cambridge, Massachusetts, designed this device; it was manufactured by the AC Spark Plug Division of General Motors.
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