You name it error.
I name it vectorial local time.
Most of the people know that:
T = T (a,g) = 2*pi*sqrt(L/|a
where g = local gravitational acceleration and a = acceleration due to the movement.
But, I repeat, you could not talk about g in the time of Galileo because the concept did not exist.
An equivalent theory to the one Newton developed could have been devised earlier, at least in theory, using the concept of vectorial local time and no forces.
Do not think in terms of Newtonian mechanics because this theory of vectorial local time, measured with pendulums, it is not based on Newtonian concepts regarding gravity.