Let me elaborate on the navigation rally first.
At its heart, navigation rally is not a race, but precision driving. The goal is to be on time, all the time.
Instructions are in the form of average speeds or leaving a waypoint at a specific time. For example, drive section 1 at 54.3 km/h. Take 3 minutes to drive section 2 (used for sections going through towns or at railway crossings), so you wait at the end of section 2 until the 3 minutes has passed.
The navigation part is by distance. For example, turn left at 0.54 km, then calibrate your odometer with the bridge at 5.1 km (except you will have to calibrate as it may scaled differently than a real odometer). You would want to keep a history of how the car entered and exited a waypoint (ie. direction and location on the way into an intersection, and the same information on the way out). This history would allow to return and make corrections in case of navigation error. The difference between bear (slight) left, turn (90 deg) left and acute (sharper) left may be important. Also, instructions may be in the form of a puzzle (ie. 6:00 on a clock face means straight ahead.).
This is very basic. As you can tell, it gets very interesting (complicated) quickly, but there are teams that can be off by only 0.1 minutes (6 seconds) after 7 or 8 hours of rallying.....
If you are interested, I can search up some links about more detail on the navigation.