'Forearm' in the Bible

(For only Og king of Bashan was left of the remnant of the [the giants known as the] Rephaim. Behold, his bed frame was a bed frame of iron; is it not in Rabbah of the Ammonites? It was nine cubits (12 ft.) long and four cubits (6 ft.) wide, using the cubit of a man [the forearm to the end of the middle finger].)

“And these are the measurements of the altar [of burnt offering] in cubits (the cubit being a [long] cubit [the length of a forearm] and a hand width): the base shall be a cubit [long] and a cubit wide, with its border on its edge all around it of a span [in width]. And this shall be the height of the base of the altar.