Setting grid properties

This is such a basic question but I’m stuck. I want to work in feet and inches and want to have minor grid lines at 1" and major at 1’. When I measure the distance between minor grid lines I get 1". But when I measure the major grid lines, I get 1’2". What am I doing wrong?

Christine

You need to set the distance between minor lines at 1”, then set the major grid lines at every 12 minor grid lines.

Thank you. I know that was really basic but I understand now.