This isn't news and it sure isn't brain surgery or rocket science.
On the back of my card I've inked marks at 1 1/2, 2 and 2 1/2 inches.
If I am at a store or train show I use my card to see how close
to scale 6', 8' and 10' an item measures.
6' is about the size of a man, 8' is about the width of a semi trailer
and 10' is about the width of a railroad car.
John