In this week's parasha, Parashas Ki Sisa, Hashem instructs Moshe to count the Jewish people by having them each donate exactly "machatzis hashekel" / "half a shekel," no more and no less. The Ohr HaChaim asks, why half a shekel? And why can't someone give more or less than the prescribed amount? Furthermore, is there a connection between the machatzis hashekel and another event in this week's parasha; the sin of the Eigel Hazahav, the sin of the golden calf?