Why use three lasers, why not just use one laser?

Using three lasers is in more than one way better than using one laser for use with ballistics. This is because scope setups in practice often experience some parallax error, even if the user is unaware of it. This is especially true if the scope is not dialed in to the correct range and if the ocular adjustment is not exactly right. This error will cause the image to move out of alignment with the reticle if the user is not looking through the center of the scope, which is not always easy to be sure of and can cause inaccuracy. So there is often some uncertainty to the exact position of a single laser dot compared with the reticle. However, with three lasers this problem never occurs because the laser dots are referenced to other lasers that are fixed beams and are not compared to the reticle. Therefore the triple laser beam positions are unaffected by scope parallax error. Three lasers also provides a clearer perception of change in distance than one laser, this is because changes in distance produce an easily perceptible change in size of the laser pattern produced on the terrain. Whereas one laser can only be viewed in reference to the position on the reticle, which is slower, less precise, subject to scope parallax error and changes in magnification adjustment. For example it is easy to see the difference between a laser pattern the size of a 20 pence piece and a single dot through quality optics. However, an equivalent difference in laser position would be imperceptible with a single laser and a scope combination. This may sound complicated but it is simple to experience in practice. Also the center of the triple laser pattern is the line of sight of the scope which is a very useful reference and the Maximum Ordinate of the pellet flight is known on activation of the device. In common parlance; three lasers are quicker to use and more precise than one laser.