I just noticed that you can get a free copy of MathCAD Express here. It comes with a free 30 day trial of the full product.
http://www.ptc.com/product/mathcad/free-trial/I have been using MathCAD on and off since the DOS version
My favorite part is that you can use units in your calculations. This gives a good check if your formula is correct. If you are calculating area and the result is in volume, you know you made a mistake.
Here is the resolution calculation for the Z axis. I only played with it for a few minutes before posting this and struggled trying to use steps as a unit.