As far as i know there is a standard that says:
1 ms = - 45 degrees
1.5 ms = 0
2 ms = + 45
but:
- the feedback of a servo is done with a potmeter, correct me if i'm wrong but they have a tolerence of 10%.
- the joystick in the transmitter is made with potmeters having the same tolereance, each channel also has a trim, again a tolerance, to my knowledge there is a adjustment inside a good (analog, don't know about digital) zeroing out the errors of the transmitter.
This leaves us in the best case with a 10% error and worst case more than 20% but planes and cars have a mechanical trimming.
To compensate all this the servos travel more +-45 degrees some even go beyond +-90 degrees.
Notice that when you buy multiple 'identical' servos that each of them will be different in behavior, one cannot just replace a servo without trimming the plane, car.... as the zero degrees position wil have shifted, there is no adjusment inside a servo.
Because in RC moddeling only +-45 degrees is used, the travel error wont be noticed, if one goes beyond specs as on this board most of us do, nothing is guarenteed.
I would propose that we search for the limits of each and every servo we use, trim the software and never exchange one servo with another to avoid retrimming of the software.
I hope this helps.
Erik