Experience my friend....I dont even use a calculator as I know exactly where the coil will measure.@raymo2u how do you calculate the resistance for the alien coils? most, if not all the free coil calculators do not go above a 2 strand core clapton coil.
Ive built these types of coils for over a year now, it comes with the territory.. Just a heads up the only thing that makes any significant difference in resistance (over a difference of .02) is the Core Wires, the outer wrap wont change more then .02 in a coils overall resistance.