Tank indicator / reserve / tank content

Hello NG, how exact is the indication of the tank contents ? according to the manual should fit in 90L if I drive according to the on-board computer until no repainting distance is timed — km. I get in when refueling max 85l. how empty can you drive the tank (without stopping) ? are at the display — km actually still 5 L in the tank ? (or possibly even more ) so you would come in case of emergency without panik (depending on the engine and driving mode ) again 30-40 km.