Which one of the following statements is not correct in respect of a prismatic compass?

1. It consists of a glass-topped case of diameter 114 mm.

2. An engine-divided aluminum ring carrying the needle rotates on a jeweled center.

3. The scale is divided around the ring from 0 to 360 degrees and half a degree in an anti clockwise direction.

4. The zero reading is engraved at the south end of the graduated ring.