Using 4"(barrel length" accounts for a factor of "two" when the sight radius is nearer 8".
Roberts calculation of a change of 0.001" = 0.22" at the target, sounds reasonable, if a pistol is shooting 4" high 4/.22= 18.2 or 18 thousandths more height required, add .018 to 0.022 original height and get a sight blade of 0.40 required.
Some how Robert made a compensating error of 10 in the calculation, since if one uses the 8.1",
one gets the 0.22"
So in this case, two wrongs Do make a right!
