Triggernometry - Reading the Wind by USAMU Coach

[CarrollMS]

https://www.ssusa.org/content/a-guide-to-high-power-rifle-wind-reading/


It is a SIN.  I think I now know how they got the values for the percent of full-value deflection based on that clock in the Appleseed Rifleman's Journal.

[Google]

Yes, fraction of full value is the sine() of the angle when measured from 12 o'clock.  There is also a diagram on page 122 of the Instructor Manual with explanation in surrounding text, although I don't believe the sine function is mentioned.

[mmirate]

This makes sense if you remember your high-school trigonometry and its central visual-aid: the unit circle.

Consider the unit circle centered at the origin of 2-dimensional space (0,0). Choosing any point (X1, Y1) != (0,0), you can extend a ray from (0,0) through (X1, Y1); that ray will intersect the unit circle once at some point (X0, Y0), and it will form an angle with another ray extended from the origin along the positive direction of the x-axis. The angle's sine is Y0 and the angle's cosine is X0, even if we only know the angle's value and not the coordinates of that point. Now (X0, Y0), being on the unit circle, has a distance from the origin of 1 unit, so X0 and Y0 are each a ratio between the scalar size of (X1, Y1) and the size of each component value X1 and Y1. All of that together, we can take any 2d vector known by angle and magnitude, and find the magnitude of the two components which are parallel and perpendicular to the zero angle.

Orienting 2-dimensional space in the most intuitive way for this application - i.e. such that the angle is between the wind direction and the shooter's line of sight to the target - the relevant component of wind force corresponds to the sine of the angle, because the x axis points downrange and the y axis points to the left or right.