There are lots of bicycle computers available. They all offer
* Current speed
* Average speed
* Maximum speed
* Total distance: the distance since installing the computer
* Trip distance: the distance since pressing the reset button
* Trip time and wallclock time
This much is standard, but also consider the differences:
* Some computers continue computing average speed and trip time when stopping while others suspend. This means that average speeds are usually not comparable, at least in town.
* Some computers retain total distance, wallclock time, and wheel diameters when exchanging batteries while others don't.
* Mechanical stability and battery life is also an issue.
* A backlight is wonderful when trying to read the display at the end of the day in a campground.
* Cadence helps developing a proper pedaling speed. 100 rpm is much less tiring than the 70 rpm beginners prefer, and easier on the knees too. After developing the proper cadence the feature becomes useless and adds an extra wire.
* Wireless computers don't need a cable running down the fork but require a clunky sensor with its own battery. They also solve the problem of failing when the socket gets wet and short-circuits the connectors.
* Temperature is neat.
* Altitude is important when riding in the mountains or hilly terrain but it seems the technology is still immature, see below. I no longer use it; instead I now ride with a Garmin Legend GPS receiver strapped to my handlebars.
* Some computers support multiple wheel diameters, useful if the same computer is used on a road bike and a mountainbike.
* Does it use a reed sensor or a sensor ring? Reed sensors work with a small magnet clamped to a spoke. They are more sensitive to vibration and can drain the battery when the bike happens to be parked with the magnet next to the sensor. Sensor rings are more precise but require a longer cable all the way down the fork.
See also an article on "avocet-cateye-vdo-casio 600"
