By setting I meant there would need to be some assurance that each manufacturer was installing the same chip or a chip that performed to the same specs in every unit. In other words in a world of say SIRF4 and GLASNOS5 for their to be unanimty between GPS units any where in the world a standard would have to be agreed that ensured each chip understood the world to have the same shape and would interpret the signal in the same way where ever the aircraft and at what ever height.
Perhaps that is already the case? Would every IFR GPS unit regardless of make report the same height every where in the world if you placed the two units side by side. I dont know?
In theory two encoders would behave in exactly the same way subject to the certified tolerance.