True that. However, what he was saying has validity. If you were to measure from the center of the left row to the center of the right row on a 4 row machine that has 36" spacing (assuming it's built accurately) then you would think "oh, I have a machine that is 9' wide". This is however, not the case. You would have a machine that is 12' wide because like he said, you have to add a half of a row width to each side of the outside row units to account for your actual machine width. The method that you and I use of just multiplying the number of rows by the row spacing and then dividing by 12 takes this fact into account. However, if the machine is not built as accurately as it could be, or you just wanted to make sure, the best way to do it would be to measure from outside row unit to outside row unit and then add a half of a row width to each side.