"Yes, Mike. But placed systematically in pre-determined places around the globe."

OK, I'm sure I'm missing something. The Earth rotates as a unit. Why are more than one instrument needed?

And if you agree that modern instruments can detect all the rotational parameters (speed, angle of axis, wobble, precession) better than your simple one can, why do you bother? Do you think the information is not made available?

The Earth's rotational parameters are known to an exquisitely fine degree of accuracy. There are no variations or "deviations" from these known or predicted motions that are gross enough for your crude instrument to measure. If any such exist, such as those likely due to gravitational waves or so-far unknown forces, they will completely escape detection by you.

Mike