yes, this is all very interesting, but it still doesn't tell us what the heck a "cubit" is.
Cubit: (k?"b?t), n. 1. (Anat.) The forearm; the ulna, a bone of the arm extending from elbow to wrist.
2. A measure of length, being the distance from the elbow to the extremity of the middle finger.
? The cubit varies in length in different countries, the Roman cubit being 17.47 inches, the Greek 18.20, the Hebrew somewhat longer, and the English 18 inches.
A cubit is a unit of linear measure, from the elbow to the tip of the longest finger of a man. This unit is commonly converted to 0.46 meters or 18 inches, although that varies with height of the man doing the measurement. There is also a “long” cubit that is longer than a regular cubit by a handbreadth. (Ezekiel 43:13)