Originally Posted by
6erwebb
I measured the chain and in 12 inches there was 25 pins exactly maesuring from pin to pin.
This is because either the first pin or the last pin is not a part of the 12 inch interval. It may make sense for you to measure from the left edge of the first pin at the zero inch mark on your ruler to the left edge of the pin that should be at 12 inches. That last pin is actually within the next 12 inch interval.
This reminds me of the old problem of why January 1 of the year 2000 was actually not the biginning of the 21st century.