 In 1953, Tuck and others suggested a number of solutions to the stability problems.This led to the design of a second series of pinch machines, led by the UK ZETA and Sceptre devices.Spitzer had planned an aggressive development project of four machines, A, B, C, and D. A and B were small research devices, C would be the prototype of a power-producing machine, and D would be the prototype of a commercial device.