Man I almost got seasick by reading those characters
Pleaze use something more "standard"
As for your calculation method, no need to wait an hour or so, just use the ruler to draw a line along the target's course and use your stopwatch to see what he does in some minutes. Then use a nomograph like the one provided in GWX, NYGM or RUB mods and that's all.
Search also in this forum for the 3 minutes and 3.15 minutes methods
