Online Calc-a-cheaters

This calculator computes the resistor divider network for most adjustable voltage regulators:

Equations:

R1= (Vo-Vr)*R2/Vr

The following is a design tool which calculates the inductance of an air core inductor. 

L= (d^2 * n^2)/(18d+40l)

where:

L is inductance in micro Henrys,
d is coil diameter in inches,
l  is coil length in inches, and
n is number of turns.