Surveyor's wheel

A surveyor's wheel, also called a clickwheel, hodometer, waywiser or perambulator is a device for measuring distance.

Origin

The origins of the surveyor's wheel are connected to the origins of the odometer. While the latter is derived to measure distances travelled by a vehicle, the former is specialized to measure distances. Much of the material on the earliest stages in the development of the hodometer are adequately covered in odometer.

In the 17^th century, the surveyor's wheel was re-introduced and used to measure distances. A single wheel is attached to a handle and the device can be pushed or pulled along by a person walking. Early devices were made of wood and may have an iron rim to provide strength. The wheels themselves would be made in the same manner as wagon wheels and often by the same makers. The measuring devices would be made by makers of scientific instruments and the device and handles would be attached to the wheel by them. The device to read the distance travelled would be mounted either near the hub of the wheel or at the top of the handle.

In some cases, double-wheel hodometers were constructed.

Modern surveyor's wheels are constructed primarily of aluminum, with solid or pneumatic tires on the wheel. Some can fold for transport or storage.

Usage of the surveyor's wheel

Each revolution of the wheel measures a specific distance, such as a yard, metre or half-rod. Thus counting revolutions with a mechanical device attached to the wheel measures the distance directly.

Surveyor's wheels will provide a measure of good accuracy on a smooth surface, such as pavement. On rough terrain, wheel slippage and bouncing can reduce the accuracy. Soft sandy or muddy soil can also affect the rolling of the wheel. As well, obstacles in the way of the path may have to be accounted for separately. Good surveyors will keep track of any circumstance on the path that can influence the accuracy of the distance measured and either measure that portion with an alternative, such as a surveyor's tape or measuring tape, or make a reasonable estimate of the correction to apply.

Surveyor's wheels are used primarily for lower accuracy surveys. They are often used by road maintenance or underground utility workers and by farmers for fast measures over distances too inconvenient to measure with a surveyor's tape.

It should be noted that the surveyor's wheel measures the distance along a surface, whereas in normal land surveying, distances between points are usually measured horizontally with vertical measurements indicated in differences in elevation. Thus conventionally surveyed distances will be less than those measured by a surveyor's wheel.

References

#Gerard L'E. Turner, "Nineteenth Century Scientific Instruments", Sotheby Publications, 1983, ISBN 0-85667-170-3
#Gerard L'E. Turner, "Antique Scientific Instruments", Blandford Press Ltd. 1980, ISBN 0-7137-1068-3

External links

* [http://www.nrw.qld.gov.au/museum/articles_complete/surveying/perambulator.html Perambulator] Information on the use of perambulators in surveying in Queensland, Australia in the 19^th century.
* [http://americanhistory.si.edu/collections/surveying/type.cfm?typeid=22 Waywisers] at the Smithsonian National Museum of American History
* [http://www.mhs.ox.ac.uk/epact/catalogue.php?ENumber=19853 Example of 16^th century German hodometer]