An odometer is an instrument used to calculate the distance from one position to another while carrying out the survey of an area. It was created in 1755 by Ben Franklin, who was a writer as well as a postman, to analyse the best routes for delivering his mail.
Types of Odometers and Working:
1.Mechanical odometers: these are turned by flexible cables which are made from a spring which are tightly wind. The cable spins inside a protective tube made of metal with a rubber housing. Regarding a car, a gear engages the output shaft of the transmission, turning the cable. The cable crawls its way up to the instrument panel, where it is connected to the input shaft of the odometer.
2. The Gearing: This odometer uses its three worm gearsto achieve its gear reduction. The input shaft moves the first worm, which drives a gear. Each full revolution of the worm only turns the gear one tooth. That gear turns another worm, which turns another gear, which turns the last worm and finally the last gear, which is hooked up to the tenth-of-a-mile indicator.
Each indicator has a series of pegs sticking out of one side, and a single row of two pegs on the other side. When the set of two pegs comes around to the white plastic gears, one of the teeth falls in between the pegs and turns with the indicator until the pegs pass. This gear also engages one of the pegs on the next bigger indicator, turning it a tenth of a revolution.
Mechanical odometers like this one are rewindable. When you run the car in reverse, the odometer can actually go backwards.
3. Computerized Odometers: In this current era, you won’t find bicycles with cable-driven odometers or speedometers. Instead, you will find bicycles with computers having a magnet attached to one of the wheels and a pickup connected to the frame. Once per revolution of the wheel, the magnet passes by the pickup, and generates a voltage in the pickup. The computer counts these voltage pulses and uses them to calculate the distance travelled.
While installing these, one has to program them with the circumference of the wheel. The circumference is the distance travelled when the wheel makes one full revolution. Each time the computer senses a pulse, it adds another wheel circumference to the total distance and updates the digital display
How to use:
- For a mechanical or gear odometer reading, you just have to roll the wheel over the distance you intend to measure.
- For a computer odometer:
Select > Odometer to view or start the odometer.
Select an option:
- Turn Off to stop the odometer.
- Reset to reset the time and distance to zero.
Civil Gadgets. 
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