Polar RC3 GPS shows altitude data it receives from the Global Positioning System (GPS). To show altitude at the beginning of a training session, the monitor needs to be connected to a minimum of 6 satellites. During training, the number of connected satellites can be fewer but if the number goes down to 0, RC3 GPS will again need the minimum of 6 satellites to re-establish altitude.
You can upgrade your RC3 GPS with the altitude feature for a fee. Please contact Polar Central Service in your country for details.