A typical fixed-power 4X telescopic sight set to have parallax-free true objective focus at 150 yards has a maximum parallax error
of 0.182 inch at 200 yards, 0.547 inch at 300 yards, and 1.27 inch at 500 yards.
Most scope manufacturers answer inquiries about parallax error
by observing that its effect is slight within the range of "normal" shooting distances for most hunting--considerably less, they say, than the accuracy variables already present in the rifle and ammo.
Most riflescopes are focused to be parallax free at 150 yards, but some have adjustable objectives that minimize parallax error
over a wide range.
Sectional times are difficult to take accurately by hand because of parallax error
, but can be measured electronically using light beams or saddle-cloth transponders.