An adjustment turret knob for a telescopic sight comprises a programmable function in which rotational positions of the knob for a specific projectile, at selected ranges, ambient atmospheric conditions, or field conditions, or any combination thereof, are stored and later used for adjusting elevation or windage settings based on the determined range of a target or conditions experienced in the field. In one exemplary embodiment, the turret knob is capable of determining, or calculating, a “best fit” trajectory curve for a specific projectile based on the stored rotational positions of the turret knob relating to the conditions under which the projectile was fired and conditions stored in memory.