The distortion produced relative to the plate thickness is known as the "K" factor (K). You can calculate the constant K factor using the following formula:
K = 2πt where π = 3.142, and t = plate thickness (minus the polyester adhesive/mylar/stickyback).
Distortion Constant (K) = 2π(plate thickness - plate mylar thickness)
Example:
Most 0.067 inch plates are on a 0.005 inch mylar so:
Plate thickness is 0.067", polyester adhesive (stickyback/mylar) is 0.005"
K= 2π (plate thickness - thickness of the polyester adhesive)
= 2π(0.067 - 0.005)
= 2 x 3.142 x 0.062
= 0.3896