A diameter tape measure can save you a lot of time and frustration when you want to find the OD (outside diameter) of a pipe, post, or tree. This special tape has the inch scale (or metric scale) stretched out by a factor of pi (3.14159). So, if you wrap it around the pipeline, you will not see the “circumference”. You will see its diameter. You don’t need to divide your answer by 3.14159.