Sigma Sport Heart Rate Altitude GPS White Rear Wheel Sensors no Power Bicycle Computers
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Heart Rate Monitoring allows a sensor, often a chest strap, to transmit your heart rate to your computer. Heart rates monitors are typically wireless.
Some computers come with built-in altimeters, which will display the current altitude. GPS enabled computers can often do this more accurately.
GPS, or Global Positioning System, is a satellite based system that provides accurate location and altitude information.
Some computers have sensors that mount to the rear wheel instead of the front, making them suitable for use with indoor trainers.
Some cycling computers can display a power reading, usually in watts. They usually require a separate sensor - in some cases a special hub or crank arm. A few will estimate the value based on speed, cadence, rider weight or other data. "Optional" means it can read from a separate power meter or sensor. "Included" means it is calculated by the computer or includes the neccessary sensor.