Commentaire sur L’Exode 26:8

שלשים באמה [THE LENGTH OF ONE CURTAIN SHALL BE] THIRTY CUBITS — so that when they place them with their length over the breadth of the Tabernacle in the same way as they put the first curtains (the length of which was 28 cubits) it follows that they are in excess by one cubit on this side and one cubit on that side, thus covering one of the two cubits of the boards left showing. The lowest cubit of the boards which no curtain covered was that cubit which was inserted in the hole of the socket, for the sockets themselves were one cubit high.