Sure.
(with delight because I love math) Note - When shooting this stage I would probably not actually do this step because I have enough data written out on the dope card to skip it. If I had only one wind speed written, then I would need this step to transition to the next target. We have 2 winds we can talk about. Actual wind speed and Cross wind speed. The actual wind speed is the the speed your wind meter gives you. The cross wind speed is the corrected speed from the wind rose due to the angle you're shooting in the actual wind. This "back calculate" is finding the
actual wind speed for this stage. If I were shooting a troop line in a straight line I would not bother with doing this, but because this stage has very different angles to the wind finding the actual wind speed can help when transitioning to other target directions.
I use the gun MPH system to do this. At 600yds (or 640 in this stage) my hold is 0.6 for each 6mph of CROSS wind. Once i shoot the first shot I can figure out what the cross wind is but I want the actual wind speed for this stage too.
Hold - Speed (at 640 yards)
0.6 - 6mph
1.2 - 12mph
1.8 - 18mph
2.4 - 24mph
(Because this is a 6mph gun, at 600yds the holds and mph happen to match up (0.1=1mph))
Cross wind = hold / 0.6 x gun mph = 2.0 / 0.6 x 6mph = 20mph
Actual wind speed = Cross wind speed / angular correction from the wind rose = 20/90% or 20/0.9 (I rounded 86% to 90% for easy math on the stage) To make this easier I work this math the other way. Rather than trying to divide by 90% (0.9) I add the remaining % to the cross wind, in this case its 10%. 100%-90% = 10%.
This is where I get the 10% from. so
Actual wind speed = 20/.9=(calculator) 22.2mph
or
Actual wind speed = Crosswind speed + (Crosswind speed * remaining %) = 20mph + 20 * 10% = 20 + 2 = 22MPH (actual wind speed)
For this stage, in my brain, rather than do the "back calculate" I would figure a % between 20 and 26mph holds. 2.0m at 640yds is half way between 1.7 (20mph) and 2.3 (26mph). On the next target I would hold halfway from 2.8 to 3.7 (1 mil so half = 0.5) = 2.8+0.5=3.2
If this didn't explain it you'll have to ask a very specific questions about this process so I can pin point a response.
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