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- so the gravitational attraction at the equator is less than at the poles (the equator is further from the earth's centre of gravity, and gravitational strength varies inversely with distance-squared)

- gravitational force slows time down (according to GR), so relative time actually passes more quickly where the relative gravitational attraction is less (i.e. on the equator)

Be careful you do not confuse gravitational attraction and gravitational potential. Gravitational attraction is the force (per unit mass) experienced by a small mass located at that point; graviational potential, however, is how much energy (per unit mass) is required to move the object from some previously defined reference point to that point. Thus, gravitational attraction is the gradient (differential) of potential.

The question therefore rises: Is the clock rate affected by the intensity of gravitational attraction, or the value of gravitational potential? I believe it is the latter, because and understanding of how gravity attracts, when examined at the quantum level, leads to the conclusion that it attracts because of a gradient in time. The gradient in the clock rate thus equates to a gradient in potential, meaning that the clock rate equates to potential. What that means is that any 2 points at the same altitude have the same clock rate, even if they do not have the same gravitational intensity. Assuming that the earth's surface is an equipotential surface (very nearly true of the oceans), the clock rate everywhere thereon must be the same -- not considering, of course, the effects of motion. Taking that into account complicates the picture in ways I do not understand.