20:7 · This ideogram is very old. It was a symbol for the moon god Nannan, later Sin, in the Euphrates-Tigris region. The sign has most likely been in use from around 2500 B.C. During the Babylonian times it appeared with and for the Venus god and the Sun god, respectively. See these signs in Group 26 and Group 25.
The structurally almost identical and appear today in astronomy and almanacs signifying the moon’s first and last quartersrespectively.
As a technical engineering sign is used for a specific type of compressor.