I don't know the scientific reasons why but these are the best rangefinder in a prairie dog town ever. Over the last 30 years we've had everything from the original Bushnell thing that we eventually nailed to a fencepost and used for target practice to the expensive binos of all the major brands. That little Swarovski works in all light and weather out to 800 yards on little targets. No ballistic program just the distance. Every time.