Units of measurement in relativistic context

In the Newtonian approximation of General Relativity, employed for the dynamical modelling in the solar system, the coordinates have the dimension of time and length. As these coordinates are close to their Newtonian counterpart, the adherence to the rules of the Quantity Calculus does not raise practical difficulties: the second and the metre should be used as their units, in an abstract conception of these units. However, the scaling of coordinate times, applied for practical reasons, generates controversies, because there is a lack of information about the metrics to which they pertain. Nevertheless, it is not satisfactory to introduce specific units for these scaled coordinate times.