C. F. Keil and Franz Delitzsch on Exodus 26:30

Exo 26:30

“And set up the dwelling according to its right, as was shown thee upon the mountain” (cf. Exo 25:9). Even the setting up and position of the dwelling were not left to human judgment, but were to be carried out כּמשׁפּטו, i.e., according to the direction corresponding to its meaning and purpose. From the description which is given of the separate portions, it is evident that the dwelling was to be set up in the direction of the four quarters of the heavens, the back being towards the west, and the entrance to the east; whilst the whole of the dwelling formed an oblong of thirty cubits long, ten broad, and ten high. The length we obtain from the twenty boards of a cubit and a half in breadth; and the breadth, by adding to the nine cubits covered by the six boards at the back, half a cubit as the inner thickness of each of the corner beams. The thickness of the corner beams is not given, but we may conjecture that on the outside which formed part of the back they were three-quarters of a cubit thick, and that half a cubit is to be taken as the thickness towards the side. In this case, on the supposition that the side beams were a quarter of a cubit thick, the inner space would be exactly ten cubits broad and thirty and a quarter long; but the surplus quarter would be taken up by the thickness of the pillars upon which the inner curtain was hung, so that the room at the back would form a perfect cube, and the one at the front an oblong of exactly twenty cubits in length, ten in breadth, and ten in height.