Relating GSR to sweating

[Dr. John Michael Smith]

I was wondering I have a GSR sensor : http://bio-medical.com/products/skin...ce-sensor.html
that takes a measure of conductance in micro - ohms.

Does anyone know an equation to relate that to how much a person perspires/ sweats ...

I've scene some stuff by Darrow, etc ...
that says its a linear relation.
but trying to derive that curve from our input is what we don't know how to do

Rob