Incorporates heavy degenerative feedback in which small lamp is nonlinear compensating resistance. Provides constant output frequency and voltage for any supply between 12 and 32 V, at temperatures down to -20 °F. Frequency is determined by capacitors C and 500-ohm trimmer control, to give choice of 100, 150, 230, and 350 cps. -H. P. Van Eckhardt,
Crevasse Detector Blazes Glacial Trails, Electronics, 31:3, p 63-65.