I just purchased a Leupold rangefinder that computes the "True Ballistic Range" to a target, based on the angle. It appears to understate the correction necessary. The manual gives an example: 400 yards at an angle of 30 degrees uphill equates to a true ballistic range of 367 yards. I've been taught that the horizontal distance to a target is what matters, and that can be computed as the line-of-sight distance times the cosine of the angle. Using that approach, the horizontal distance is 346 yards. Can someone please point me in a direction to better understand how the distance when shooting at an angle should be computed? Is the Leupold algorithm correct?

I have a Leupold range finder and have tested it to see if it was on the money,close or way off. Mine appears to be very close based on the test I performed. The first time I carried it to Colorado I wanted to be sure it was correct and got the opportunity to find out By using a vertical bluff to calculate the TBR. I had checked out the range finder at the range on known distances.100,200,300,400,500 and 600yards. It was dead on in fact if I took one step forward or backwards the range finder would make the correction ether way. So when I tested using the bluff I simply ranged the face of the bluff at eye level from the same distance as the range 100, 200, 300, and so on. then ranged the top of the bluff and wrote down the TBR and later back at camp did the math and it was very close + or - a few yards. I even checked it out in the archery mode again it was very close. With the horizontal range and the Hypotenuse I was able to calculate the height of the bluff and later verify it when on top and looking down at the level ground where I stood and took all of my readings. and they all agreed using all the readings and doing the math. The Leupold like most range finders are not perfect but they are so close it doesn't mater. J E CUSTOM