Just like a reticle in a sniper rifle, the Rangefinder in Spyglass is based on the height of an average human, which is 1.7 m or 5.6 ft, and is used to visually measure the distance to your target. E.g. a person, a deer, some other creature or object of a similar height. So let’s see how it works. The scale shows the distance from 100 to 500 m with a 50-meter step. And we will use a person as an example. Zoom for higher precision. And if the person fits between the rightmost upper and lower marks, the distance to them is 100 m. If they fit between the leftmost upper and lower marks, the distance to them would be 500 m. And everything in between could be easily measured in your mind with the help of 50-meter steps.