There are two main methods for inputting a wind value and calculating a solution. Lets first differentiate a “light” solution generally used for quick shots under 1000 yards and a full “vector” solution for complete ballistic calculation.
The light solution uses an input method that we call Base Wind. The Base Wind method calculates a solution based on a shooter relative wind of either 9 o'clock or 3 o'clock. Because the wind solution is bi-directional, other calculations that require specific directional inputs or combined output values must be disregarded. Fortunately, for the closer ranges that light solution is used, the other calculations are negligible.
Calculations that require a directional input:
Aerodynamic Jump
Headwind/Tailwind
Spin Drift
Coriolis
For example, the spin drift for a right hand twist rifle will always be to the right. Approximate magnitude at 1000 yards is 10 inches (or 1 MOA), depending on twist rate and a few other variables. If we have a 9 o'clock wind at 10 mph, and we are shooting a typical long range cartridge at 1000 yards, the bullet will drift about 4 MOA to the right. The combined solution for windage correction would be 5 MOA to the left. If the wind was from 3 o'clock, the combined solution would be 3 MOA to the right. This is why we cannot use Spin Drift when using a Base Wind light solution.
For Aerodynamic Jump, the calculation routine requires a vector wind input because (assuming a right twist barrel, which comprises the vast majority of rifles) a left wind causes an elevation point of impact shift down, and a right wind causes an elevation point of impact shift up. With the light method, we cannot specify a direction, therefore we cannot use the vector routine.
Coriolis is a very small factor that changes the left/right point of impact with change in Latitude. Because the light solution is bi directional, the correction cannot be combined.
With a Vector Solution, the wind direction is input, and a directional solution is calculated, therefore the user can enable all three of the above mentioned calculations.
There are two types of vector solution methods that only vary based on the coordinate reference system. The global reference system uses the azimuth of the wind source and must be combined with the target azimuth to calculate the shooter-relative wind correction. The second reference system is just shooter relative. We differentiate these methods by using degrees for global units, and clock position for shooter relative.
The rosette or wind clock in the BR4 display should always show a shooter relative wind direction. If a base wind is displayed, the 9 o'clock and 3 o'clock arrows are simultaneously illuminated.
The two methods in the Revic Ballistic Ecosystem
Vector Wind - The shooter-relative wind vector is input
Base Wind - A direction-independent full value wind solution from Left or Right
Base wind is now a part of your programmed ballistic Profile. All future devices will read base wind from the Profile. In the current BR4 rangefinder, base wind is a global device setting along with Earth based effects, Aerodynamic Jump routines, and Spin Drift.
Be aware of your advanced calculation settings and the resulting limits on solver accuracy. Base wind is an excellent method for fast corrections within the appropriate limits. Personally, with my hunting cartridges, I try to operate within 800 yards for Base wind solutions. Any farther, and I’ll input my wind vector data.