Modern laser rangefinders work using "time of flight". The speed of light is constant. The laser rangefinder fires short pulses of invisible laser light at a target through the small lens. The big lens receives the bounced back signal, and based on the time it took for the signal to return, the rangefinder calculates the distance. It also has an angle sensor inside, not unlike a carpenters' level. It then adjusts the distance using the angle to provide the user true horizontal distance.

We packaged this system in a comfortable, arm worn package. You simply place the Neverguess on your arm, attach the switch to your finger, and adjust it to your draw posture.

The NeverGuess has fiber optic sights that allow you to aim it at the target. You squeeze the switch against your bow handle, and it displays the true horizontal distance to the target.