Hi Richard, Thankyou for the worksheets. I didn't realise you could do it that way, much cleaner! I seem to have a 'Floating Point Error' with it at the moment, just trying to track it down at the moment.
Changing the precision in the Evaluate menu removes the error. However, the values returned for SX, SY, ... , u3 are unchanged from their original values. Will dig into it some more :-)
Ahhh.... Ok, changing the FP precision resets the method to Conjugate Gradient. Changing to LM brings up the 'Encountered a floating point error' issue. Will keep looking...