The measuring wheel is a device consisting of a wheel of known circumference with a handle attached by which the wheel can be pulled or pushed and a device which measures the number of times the wheel turns on the ground.
The measuring wheel has been in use for hundreds of years. It was re-introduced as a device for measuring distances in the 17th century. The earliest devices were made of wood and some of them had iron rims to provide strength and durability. They were made like wagon wheels and often by the same makers. Modern measuring wheels are made of aluminum with tires on the wheel.
How the measuring wheel works
This device operates on a simple principle: since the circumference of the wheel is known, the distance covered by the wheel is equal to circumference of the wheel multiplied by the number of times the wheel turns. For example if the circumference of the wheel is 1meter and the wheel turns 100 times in moving from A to B, then the distance between A and B is 1meter multiplied by 100 which is 100meters.
Note: Circumference means the distance round a circle
If the wheel makes an incomplete turn or the number of turns is not a whole number, the distance is measured using the same principle. For example, if the wheel turns 50 times and then makes a ¾ turn, the distance is measured as 1meter multiplied by 50¾ which is 50¾meters or 50.75 meters. The wheel is marked round in segments starting with a reference point, so a fractional turn can be observed easily.
Uses and limitations of the measuring wheel
The measuring wheel is used primarily for lower accuracy surveys by farmers, underground utility workers or road maintenance crews for quick measurement of distances too long to be measured conveniently with a measuring tape.
Distances measured by the measuring wheel are usually longer than those recorded in conventional land surveying because the wheel measures the distance along a surface while in land survey, the distance between points is measured horizontally.
The measuring wheel gives a fairly accurate measurement on a smooth surface, such as pavement but on rough ground, it could bounce, slip or climb over obstacles on its path, all of which reduce its accuracy by either adding to or reducing the real distance covered. Soft sandy or muddy soil can also affect the turning of the wheel. For a more accurate measurement, take note of any circumstance along the path of the wheel that could affect accuracy and either measure it separately (with a tape or some other instrument) or correct for it mathematically.
Various modifications of the wheel are in use today, with more sophisticated measuring devices and some of them can even be folded up for easy transportation but the principle by which they operate remains the same. These modifications vary according to the kind of professionals who use them.