Text copied from TM9-1985-2 German Explosive Ordnance 1953 :
Description: The body is an aluminium casting which in its upper portion houses the clock, and in its lower portion the striker mechanism. The top is closed by a screwed cap with a rubber ring washer below it and into the base is screwed the cap holder having leather washers as shown. A key is provided for screwing home this holder. On removing the cover the clock is exposed. The knurled cylinder is provided for winding the clock while the center knob marked stamped Zt, is for setting the clock for any desired delay up to 21 days. The minimun delay is ¼ hour. The delay times are marked on the edges of the disks; the days figured in red, ad the hours figured in black. The setting is visible through the window and is indicated by the pin. This latter is connected with the lever arm which allows the trip lever to release the striker at the end of the delay period. At the 24-hour marking on the black-inscribed disk and at the 21-day marking on the red-inscribed disk are slots which allow the pin to move into the channel. These slots are aligned at the zero reading at which position the striker is released. The slot in the disk is covered by a lightly-sprung steel strip which is pushed back by the pin as the clock approaches the zero setting. At this strip can only be pushed in one direction, it provides a safety device to prevent the striker being released while the clock is being set by the knob. A further safety device for the preservation of the clock mechanism is provided by the bend steel wire. This passes through, and is secured to, the spindle, so that when the latter rotates with the lever at the end of the delay period the short limb of this steel wire presses against the balance wheel and stops the clock. If this was not provided the clock could continue working and by further rotation of the disks, the pin would jam or would be deformed. This is important since provision is made for testing the clock and its though that the clock mechanism may be intended for re-use. The clock is started by the movement of the ring through an angle of about 30°. Two screws, passing through the ring, project into the clock mechanism. Between them is the lever arm to which is attached a thin spring steel strip. In the stop (steht) position this latter is in contact with the balance wheel of the clock and holds it. When the red mark on the ring is moved to the go (geht) position the lever moves the steel strip so that it gives motion to the balance wheel and then moves clear of it. The ring is held by either the "stop" or "go" positions by the shaped steel spring, ad the lever arm is held by the shaped spring. The striker mechanism is retained in the body by the four screws. The striker is held in the cocked position by the trip lever. The movable piece is a transport safety device. In the "safe" position this is pushed over by the spring strip so that the striker is prevented from reaching the cap. The screw marked "scharf" replaces this when the apparatus is set for action. The stem of this screw projects far enough into the striker mechanism to push over the movable safety piece to allow the full movement of the striker when released. The accessory is provided with the equipment. It screws in, in place of the cap holder, ad is to be used for recocking the striker after test or after use.
Operation: At the end of the delay period, the lever arm on the rotating control disk bears against the trip lever, causing it to release the striker. The striker, driven by the striker spring, is then forced into the percussion cap, firing it.
Employment: Used for large scale delayed demolitions. Delays are possible from ¼ hour to 21 days.