What eventually this will be for, is the tuning element of an antenna for 630 meters. I saw another ham's project on-line for a homebrew variometer, which is comprised of two inductors, wound as spheres, one inside the other, the outer one stationary, the inner one rotatable for aiding/opposing. Picture it like you had a globe, and started winding at the south arctic circle in a spiral up to the north arctic circle. So, an inductor, but wound on a ball, not a tube. And with a smaller one inside of that. And the two connected in series. Rotate the inner and it aids or opposes by varying degrees. A variometer. So then, how to predict in advance the inductance in uH? I'm thinking to calculate it as if the same length of wire were wound an equal number of times for the same length of run on a tube whose diameter is the average of all the windings on the globe. I have a script, written in Perl, for calculating turns, spacing, and length of wire for any size globe. And it also attempts to make a prediction for inductance based on above. But until I build and measure it, I'll not know for sure. Anyone else tried something similar?