This calculator was created to accompany our new book on SPICE simulation of guitar amplifier circuits.1 At one point in writing a large-signal triode model, a curve fit is required using quadratic regression. As a convenience for readers of the book, this calculator performs these calculations automatically. Specifically, the calculator computes optimal values of K1, K2, and K3 for the formula
A = K1(VG)2 + K2(VG) + K3
The algorithm requires at least 3 data points and handles up to 9 data points. Leave unused inputs equal to "0".