We got lots of questions about a tool we sell called a "Planimeter". Many people pronounce the word plan-eye-meter, or pa-lemeter, but we're fairly sure either way to pronounce the word is acceptable within the industry.
What are Planimeters? They are tools used by anyone that wants to measure an irregular area of an object. Since a planimeter rolls around on a flat surface, the object being measured is usually on paper, or an x-ray, or something that can be copied on a copy machine and then the area measured from the flat copy. I've seen people lay an object on a copy machine, run a copy, then use a planimeter on the copy to calculate the area. I've heard of medical technicians measuring tumors on x-rays, shoe manufacturers taking a shoe apart and measuring the area of the leather panels and doing so on a new shoe, and a shoe that has been worn for months which measures the stretch of the leather. I've heard of many uses of planimeters. Personally the most use I ever experienced with a planimeter was to measure the each contour line on a topo map of a detention pond design to see get the volume of the pond. I would get the area of each closed "loop" (contour line) and then use those to figure the pond volume. That was back when I was doing drainage calcs, cut and fill calcs, and other civil engineering related design projects. Remember, if you want to figure the area of a regular shape like a rectangle, or square, that's easy, you simply multiply length x width to get area. But for irregular shapes like ponds, custom swimming pools, golf course greens and sand trap designs, you'll need a planimeter and a "closed loop" to measure.
How Do Planimeters Work?
Planimeters work off of rolling around on the flat surface that's being measured. They have small wheels or rollers (hence sometimes you'll hear someone refer to them as a "Roller Planimeter") that roll and the planimeter itself will figure the distance traveled on the flat surface and then compute the closed loop area measured into data. That data is then converted using a multiplier for the scale drawing (i.e. 1"=50', 1/4"=1'). Don't worry, planimeters usually come with a user manual and they are easy enough to understand and teach yourself how to use one. We've never had anyone return a planimeter because of difficulty in learning how to use one. From there, you break planimeters down into two categories, mechanical and digital (sometimes called electronic). Both types have the small wheels or rollers, but the mechanical does not have batteries or any electrical parts. The mechanical planimeter has a vernier or tick marks on a meter that you reference and then multiply the data against a multiplier (using your hand calculator) to get area. An electronic, or digital, planimeter you enter the scale of your drawing into the planimeters keyboard and it figures the math for you. I recommend mechanical planimeters for people that use one say 3 to 5 times per month. I recommend digital (electronic) planimeters to people that do at least 3 to 5 uses per week.
Hopefully this article teaches the basics of what a planimeter is, who uses them, and how they work.
Rob Powell of EngineerSupply
