reed switch, is attached to the fork or the rear of the frame. The sensor detects when the magnet passes once per rotation of the wheel and time stamps or time codes the revolution count. Alternatively, a sensor may be attached to the wheel hub. Distance is determined by counting the number of rotations, which translates into the number of wheel circumferences passed. Speed is calculated from distance against lapsed time period using the circumference of the wheel and the time it took to make one rotation. The cadence sensor To measure cadence (revolutions per minute of the crankarm), a magnet is mounted to the crankarm, and a sensor mounted to the frame. This works on the same principle as the speedometer function and measures the turning of the cranks and front chain ring. Transmission Some models use a wired connection between the sensor and the head unit. Other cyclocomputers, e.g. those used by competitive cyclists, transmit the data wirelessly from the sensor/transmitter to the head unit. Data can be exported to a SD card, computer, or phone and uploaded to an internet web service. Wireless cadence and speed sensors use wireless communication standards ANT + and Bluetooth Low Energy and can directly communicate with a smartphone application that also uses the phone's GPS, barometer, temperature, clock, and other sensors to create a more detailed picture, record, or map. Calibration Once a new computer is installed, it usually requires proper configuration. This normally includes selecting distance units (kilometers vs. miles) and the circumference of the wheel. Since the sensor measures wheel rotation, different wheel sizes will translate to different measures of speed and distance for a given number of rotations. For more accuracy the bicycle (with the set cyclocomputer) must be ridden by the intended rider over an accurately measured distance. The computer's reading is then compared with the known distance and any necessary corrections made. Additional information Besides variables calculated from the rotating wheels or crank, cyclocomputers can display other information. Gear For integrated shifters on racing bicycles, the gear can be read by the computer: Shimano's Flight Deck and Campagnolo's ErgoBrain work with their respective systems to detect the gearing. This allows indirect measurement of cadence. These systems do not have sensors on the crankset or cassette to determine what gear the bicycle is in. They work exclusively with the shifters, which may result in misleading information. Instead