And to add a simple riding example... it is usually measured as being "in range" between two mV settings and somewhere within this range it will feel optimised when initially rolling on and off the throttle. There is a bit of testing for the settings and the movement of the TPS in this range is very small.
Checking it is a simple part of optimising the smooth throttle action of the bike and is often neglected by many techs/mechanics. As a bike gets used and wears it will obviously be more prone to change from the factory setting.
If you search for "TPS" or "throttle position sensor" you will eventually find some good information. Obviously pros like Steptoe will give you the best info so so look his posts or similar and filter out the guessers...