Locate an object on the other side of a river. Stand on your side and point the direction-of-travel arrow towards the object. Align the magnetic needle to 45O indicator of the compass housing. Pace the line BC while pointing the direction-of-travel arrow towards the object all the time. Point C is marked when the compass is oriented (magnetic needle is directly above the orienteering arrow). The distance BC is a rough estimate of distance AC. You have just formed a 45-45-90 triangle, which has two of its sides equal to each other.