The measuring rod in the book of Ezekiel was 6 long cubits of 7 palms and equal to 7 cubits of 6 palms.
The standard biblical cubit was 6 palms, and is well described in the book of Ezekiel.
The biblical 'long cubit' was a cubit and a palm, and 6 plus 1 equals 7.
The common or ordinary Egyptian cubit, now labelled the royal cubit, had 7 palms.
Sir Isaac Newton thought that the Egyptian cubit used at Giza had 6 palms, but he was wrong. Greaves' incorrect drawing of the Grand Gallery showed six overlaps on the side walls, but there are actually seven.
Take the standard cubit, from elbow to finger tip of middle finger, as equal to 6 palms:
For casual measurements in long cubits start by placing the palm of the right hand behind the elbow of the left arm as the first long cubit; then transfer the palm of the right hand to the middle finger of the left arm, followed by the cubit of the left arm for the second long cubit.
I often use my feet for measurement when doing sketches and casual surveys of engineering plant, and did so just last week. The long cubit was a practical tool for measurements. I have found that I can measure very quickly along a wall or on the top of a bench in 'long cubits'. Measurements are surprisingly quick and accurate in long cubits, palms and digits, and easy to convert to inches or metres if you know the length of your cubit, and the width of your palm.
It is extremely difficult to measure in standard cubits without a measuring rod, as it is difficult to see behind the back of the elbow.
The biblical long cubit has the same biological basis as the Egyptian royal cubit, but this does not mean that it was exactly the same length.
Mark