The radio

The radio grants you to keep sights of your units in range with the radio at the time it read the positions.
You can also communicate with other allied radios, to get their readings for your section.
In both cases, the reading will be saved for 3 days on your map.

Each time you get reading from your section or from the other radios, your map will change with the most accurate reading for each cell in range of sight.

When you get your positions :

The best way to have good readings is to observe with a scout unit, then read your positions with your radio. As the observation lasts for only a couple of hours, doing this grants you to keep tracks of the battlefields for a much longer time.

Limits :

As a strategy tip, you have 4 issues with the radio :

Earning something :