Adam Clarke on 2 Chronicles 3:3

The length - after the first measure was threescore cubits - It is supposed that the first measure means the cubit used in the time of Moses, contradistinguished from that used in Babylon, and which the Israelites used after their return from captivity; and, as the books of Chronicles were written after the captivity, it was necessary for the writer to make this remark, lest it should be thought that the measurement was by the Babylonish cubit, which was a palm or one-sixth shorter than the cubit of Moses. See the same distinction observed by Ezekiel, Eze 40:5 (note); Eze 43:13 (note).