The Tomahawk and Arrowhead LPVO optics have a diopter adjustment to optimize the focus of the optic for individual vision. The diopter adjustment ring determines the focus inside of the optic, ensuring the image is in sharp focus to your eye for maximum clarity and accuracy.
Proper adjustment is based on individual eyesight and will vary from one individual to another. Adjusting the diopter will marginally change the magnification of the optic. This will not have a significant effect on the subtention measurements of the reticle.