The J device, no1 (J Gerate Eins) or Muller Mechanical Integrating Accelorometer. © THBC

The J device no1 (J Gerate Eins). The full name of this device is: the Muller Pendulous (or mechanical) Integrating Gyroscopic Accelerometer - today normally referred to as a PIGA. The device, designed by Fritz K Muller, operates as a switch to initiate rocket engine shutdown and is able to smoothly record and accumulate every moment of acceleration, without any kind of recording resolution or discrete time interval limit, of the rocket's entire motor burn phase, and at the same time process this accumulated acceleration with respect to time as a gradually increasing velocity. In the case of the V2 missile, when the correct predetermined velocity is reached, the velicity sufficient to achieve the desired range of the missile, the device trips the relays that close valves that shutdown the supply of steam to the turbo-pump, and thus shutdown the rocket motor itself.