Yes and No, or is it No and yes?
I am not home right now, but to answer your question, no you can't use a NAPA transducer (99.999% sure). You could come up with your own transducer, but it takes more than just buying a transducer off the shelf, since the GRT4000 uses biased 5 voltages, not just ground resistance. Also a transducer sensitive, with proper quality and range will not be cheap. Not knowing the exact specs of a NAPA unit (or if one can be bought) will be hit or miss; I suggest you buy the GRT MP unit made for this purpose.
When you purchase the GRT MP transducer you will be given the info, SF and offset. It uses one of the AUX inputs. It is not a standard option so you may not see specific info on the MP in the manual, but the instructions do tell you how to set up an AUX input (label, decimal location, scale factor (SF), offset. In fact the MP is calibrated and has the info right on the "box".
Let me know if you need further help, but you will have to wait till they open. May be you can order on line and back-up the order with a call First of the year. Good Luck George
