An accurate measurement is vital when ordering a new door unit and using a tape measure to record accurate dimensions is key to a ordering a unit that will last for years.
A standard tape measure in the United States uses inches as the base for measurement with sixteen tick marks in between each inch marker. The smallest tick marks denote the odd numbered sixteenth marks such as 1/16, 3/16 up to 15/16.
Between the odd numbered sixteenth tick marks are longer tick marks noting even numbers. In order to make measurements easier to remember and record, each even tick mark is divided by two until it reaches its lowest common denominator. So, 2/16 is divisible by 2 down to 1/8, 6/16 to 3/8, 10/16 to 5/8 and 14/16 to 7/8.
The next longest tick marks of 4/16 and 12/16 are each divisible by 2 twice down to 1/4 and 3/4.
And finally 8/16 is divisible by 2 down to 1/2.