When I was preparing the list above, I was trying to get to the very fundamental measurements that all sellers should be able to make.
Simple things such as wheel base and how high off the ground the top tube is can be directly measured. Wheel size can be determined by reading the sidewall of the tire. Anyone of average intelligence can do these things.
1. Spin the crank to get the pedals out of the way, point the front wheel straight ahead and measure the wheelbase using a tape measure.
2. Measure the vertical height from the top of the top tube to the ground with that same tape measure.
3. Read the sidewall of the tire and report the tire size.
Tube lengths, frame angles, stay lengths, etc are more esoteric and did not make my list. Some of you know enough to report these but I do not expect the average Joe to do so.