High School Am I understanding the concept of proper frame of reference?

[PAllen]

I'm not sure I see this implication, since the section that discusses this for curved spacetime (13.6) refers to Exercise 6.8 which defines an accelerated rotating frame for flat spacetime, and says that this section will do the same for curved spacetime. There is no reference anywhere that I can see for a use of the term "proper reference frame" to describe a standard inertial frame in flat spacetime.

That said, I agree that zero acceleration and zero rotation can be plugged into the equations as a special case, and yield a standard inertial frame (in curved spacetime, a local inertial frame), and that MTW does include that special case.

I found an explicit statement in this section of MTW (13.6 bottom of p. 331 in my edition) that makes clear that they have the meaning I claim:

" In the case of zero acceleration and zero rotation, (..), the observer's proper reference frame reduces to a local Lorentz frame (...) all along his geodesic world line!"