Clocks show less elapsed time in gravitational field right? So clocks on Earth seem to apply. Consider one clock stationed on the north pole and one somewhere on the equator, both at sea level. It seems there are a couple of factors in order to calculate the difference in time between each clock and a fictional observer in flat space. Looks like we have to take into consideration the following things They are in a gravitational field The EM-force accelerates in the opposite direction The Earth is rotating, Both clocks are accelerating due to the rotation (each one slightly different). The earth is not a perfect sphere. My main question concerning this problem is the "cancellation" of the EM-force. How does the EM force interact with the curvature? Are there well established theories for this?