Currently reading the following document which is a bit of a brain overload at the minute! Im considering Equation (4.61). It is the general relativistic correction due to the Schwarzschild field for a near Earth satellite when the parameters [itex] \beta, \;\gamma \equiv 1[/itex]. However, as you will see, for the equations of motion they use geocentric coordinate time as the independent variable instead of the proper time as is usually the case. This is also the same for the IERS convention given here by equation 10.12. Has anyone seen this before? I am struggling to get my head around this.