I have checked out Four-Colour and a few other on-line calculators but they are all way too complicated for me. I was hoping to find a simple calculator where I can just plug in my X and Y coordinates of the field and reference meters, but that does not seem to be the case. When I look at the math behind the calculations, only PHDs and the like will be able to understand it. Been at this for 4 nights straight but I just can't get past this point.I use HCFR to calculate the matrix. There are also some online calculators that can calculate the correction matrix. Search for Four-Colour Correction Matrix.