The Speed Drop Factor: elevation you dial from memory, and how accurate it is.
Elevation (mil) = distance / 100 − factor.
With a 2-click tolerance, a .338 stays within 15 cm from 325 to 875 m.
You give up a little precision and gain time.
It is the feature military units value most, tested many times in training courses: one number to remember to dial elevation from memory, without looking at the screen.
Every rifle and ammunition combination has its own Speed Drop Factor. With that number, you work out elevation in your head:
Example with a factor of 2.3: at 600 meters the elevation is 6 − 2.3 = 3.7 mil; at 800 meters, 8 − 2.3 = 5.7 mil.
The rule is not exact at every distance: it holds over a band of working distances, within the tolerance you choose. With our .338:
| Tolerance | Factor | Distance band | Maximum error |
|---|---|---|---|
| 1 click (0.1 mil) | 2.4 | 400 to 825 m | 11 cm |
| 2 clicks (0.2 mil) | 2.3 | 325 to 875 m | 15 cm |
With a 2-click tolerance, the most common choice, a single number covers 550 meters of distances. Outside the band the error grows: 11 cm at 250 meters, 67 cm at 1000 meters.
.338 Lapua Magnum, 250-grain bullet, 900 m/s, G7 BC 0.31, scope 6.85 cm above the bore, 100 m zero, 15 °C, 1013 hPa, 50% humidity.
Where speed matters, as in an operational setting, you give up a little precision and gain time: no screen to check, just one subtraction. Where every centimeter counts, you use the full firing solution.
The factor changes with caliber, bullet, velocity and the tolerance you choose. The app calculates it for your profile, shows you the distance band where it holds, and prints it for you, together with the Quick Wind Factor for wind.
