Matthew Poole and continuators on Exodus 30:13

13 This they shall give, every one that passeth among them that are numbred half a shekel, after the shekel of the sanctuary , (a shekel is twenty gerahs:) an half shekel shall be the offering of the LORD .

Which though it hath been commonly conceived to be double to the common shekel, yet divers late learned men seem more truely to judge that it was no more than the common shekel consisting of half a crown of English-money, which is called the shekel of the Sanctuary because the standard by which all shekels were to be examined was kept in the Sanctuary, as afterwards the just weights and measures were kept in Christian Temples or other publick places. See Levit. 27. 25. Numb. 3. 47. Ezek. 45. 10, 11, 12. add to this, that it was a part of the Priests office to look to the weights and measures, as plainly appears from 1 Chron. 23. 29.

Not less, least it should be contemptible, nor more, least it should be too burdensome for the poor.

Marginal references: Matth. 17. 24.