The ZE IV is a 45-day mechanical, spring-driven, sterilizing clock designed for use in the OMA mine. The clock is set by rotating the dial counterclockwise to the desired period opposite the red arrow. At the end of the clock's run, lug A, figure 280, trips spring-retained rocker arm B, which rotates lever cam C, releasing spring-loaded striker D. This clock was not used operationally because the time period was considered too short.

Figure 279 – ZE IV

Figure 280 – Diagram of ZE IV