Wolfram Research
Wolfram Math World: Point Plane Distance
Find the distance between a point and a plane using the algebraic formula for the plane and the Cartesian points. This MathWorld page has a labeled diagram to help clarify the equation variables.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Distance From a Point to a Plane
Use this site to findout how to find the distance from a point to a plane.