I've read through several of the forums regarding how errors for ground control points are reported and still don't quite understand how the errors are being calculated.

From what I've read, the total error reported at the bottom of each column is essentially RMSE ("square root from the sum of squares and that's all is divided by the number of GCPs"). Is this correct?

I've put my GCP error values into an excel table and no matter how I try to calculate total error for each column (x,y, and z), or the error values in the 5th column, I can't get the numbers even close to matching.

Would someone please help explain how PS calculates these values?

Thanks in advance.