L1\L2 Button.
This allows you to input two locations, for example if you was at an airfield you could add the airfield name as location 1 and OTT airfield name in location 2.
To show the Location boxes long press the L1/L2 button, long press again to hide the locations
Once entered you can switch locations by tapping L1 and it will change to L2 with the location changing accordingly.
The images below show i have Shawbury and OTT Shawbury entered in the location boxes,