There were evidently shekels of more than one weight at the time. This specified which one was to be used. See how you translated this in [Exodus 30:13](../30/13.md). (See: [[rc://en/ta/man/translate/translate-bweight]])
Translators may use units that people know and round numbers: "3.7 liters" or "four liters" (See: [[rc://en/ta/man/translate/translate-bvolume]] and [[rc://en/ta/man/translate/translate-fraction]])