1 foot = 12 inches
42 feet = (42 x 12) = 504
The factor of (6 inches / 42 feet) is (6 inches / 504 inches) = 1 / 84 .
The scale factor is not in inches. It's a factor, and has no units.
A 1-ft model would represent a real 84 feet.
A 1-meter model would represent a real 84 meters.
A 1-yard model would represent a real 84 yards.
