There is no difference in function or accuracy. The only difference is the type of sensor to replace to calibrate the unit.
To check which type of sensor you have, you'll need to first open the sensor slot on the back of the device and remove the sensor
Pressure - with red, black and white wires.
Non-pressure - without wires.
The non-pressure sensor wont work in the unit that requires a pressure sensor, and vice versa. Should you still remain unsure which you can contact us by clicking on "New Support Ticket" above