AVYD is a Visual Yardage Designator to measure distance to your target by means of visually confirming the target with a laser designator. (distance displayed in yards) AVYD can be temporarily connected to any bow or crossbow by means of the included universal clamping system. No alignment or calibration is required and set up takes less than 60 seconds. (clamping to the riser or stabilizer is most common) IMPORTANT: because AVYD uses a visual laser designator its effective use and range is limited to times when you do not have direct sunlight interfering. AVYD works as designed the first two and last two hours of shooting light and more depending upon how much tree cover you are in. And like all handheld rangefinders you must hold the unit relatively still and on-target to get a good read. Effective distance is out to about 60 yards. Get AVYD now with FREE EXPRESS SHIPPING!!! 1 year of battery life with included CR2 battery Laser radiation; Avoid direct eye exposure Output power: Class IIIR Laser <5mw; Wavelength: 630-640nm; Beam divergence: <1 mrad IEC 60825-1:2014; complies with 21 CFR 2040.11 except for deviations pursuant to laser notice 50, 6/24/2007