Dustproof/water resistant at depth equal to or greater than 1 meter.
Resistance to sweat makes it ideal for use while doing sports.
The device has an electronic display to present information to the user.
These devices will not experience water damage, e.g. in the shower. Devices which can withstand more water pressure are better for swimming or diving.
Polar RCX3 GPS
This measures barometric air pressure. It can predict weather changes, for example a sudden drop in air pressure could mean a storm is coming. When calibrated correctly it can be used to determine altitude, which helps GPS devices to lock on quicker and with greater accuracy.
It can detect changes in elevation, such as when you are climbing stairs.
An indicator shows you when the device has low battery.
A solar battery takes its energy from light, and stores it in a self-recharging battery which never needs to be changed.
With a stopwatch you can time yourself.
With a world timer you can easily see the time all over the globe. It is useful if you are travelling through different time zones.