The Google homepage today features a graphic on Romer and his conclusion. As he used the Equation of Time in his conclusions it means the predictions are skewed by the calendar framework, that a full set of tables didn't arrive until the time of John Harrison and that the Equation tables are discontinuous for each 4 year tranche to the next for very specific dynamical reasons.I am only sorry that there are no adults around who can discuss the technical details but that is simply a personal matter that I absorb.
The motion of Io and the other satellites around the parent planet Jupiter acts as a secondary aid to judging the motions of Venus and Mercury around the parent Sun -
https://www.youtube.com/watch?v=FcrBAuLBXag
We see Venus and Mercury run their circuits in much the same way as they move to their widest point as seen from a slower moving Earth before turning in front of the Sun -
https://www.youtube.com/watch?v=MdFrE7hWj0A
The Earth's orbital motion sets the Sun up as a central reference by using the change in the background stars to the Sun much like an object is hidden behind the center of a large traffic roundabout as a car moves along the lane hence the stars ElNath,Castor and Pollux process the same function.
Romer's procedure is dysfunctional and entirely inappropriate for 21st century visual observations and the huge conclusions which are awaiting those who can take a step back and see the partitioning of retrograde resolutions takes priority as the inner planets use a separate proof of a moving Earth than the slower moving outer planets. No doubt man want to live with the problems created by late 17th century modelling using timekeeping and the calendar framework but this is typically small