This enables the shooter to follow the projectile trajectory in order to make aiming corrections.

Signallers, or spotters, watched where each artillery shell landed, then sent back aiming corrections so that the next shells could hit their targets more accurately.

Even with a 13.09 mil canted mount the employed sighting system is not able to dial in over 39.09 milliradian of vertical aiming correction, which is significantly less than Harrison required during his record shot.

Harrison had to use the P4 reticle offering 0.5 mil spaced holdover hash marks in his 5-25x56 telescopic sight to compensate for the lack of vertical aiming correction and thus achieve the required aiming solution.