cutting ruler lines

[kpattondesigns]

Hi
I am trying to "cut" the lines and numbers for a Growth Chart Ruler. I want it to measure 6', I also want it to include
the 11 lines between each foot.

my issue is the lines do not match up as exact/true measurements when comparing it to a measuring tape.
the more "feet" I add the measurements get "off kilter" and by the end of the 6' it is totally off exact/true measurement.

Can you help me understand how to get a "cut" with "inch lines" that will measure 72" or 84" and be exact?

I hope I explained that correctly and intelligently.
thank you