Let’s follow the orbit of a particle or the route of a vehicle as a curvilinear function with associated directions at every point. Measurement produces travel distance *r*, travel time *t*, with directions *θ* and *φ*. The directions may be considered as functions of either travel distance or travel time: *θ*_{r}, *φ*_{r}, *θ*_{t}, or *φ*_{t}. There are accordingly four possibilities:

(*r*, *t*, *θ*_{r}, *φ*_{r}), (*r*, *t*, *θ*_{t}, *φ*_{t}), or (*t*, *r*, *θ*_{r}, *φ*_{t}), or (*t*, *r*, *θ*_{t}, *φ*_{r}).

The latter two may be made equal by a change of convention for measuring the angle. These may be represented rectilinearly as:

(*t*, *r*_{x}, *r*_{y}, *r*_{z}), (*r*, *t*_{x}, *t*_{y}, *t*_{z}), (*r*_{w}, *r*_{x}, *t*_{y}, *t*_{z}), or (*t*_{w}, *t*_{x}, *r*_{y}, *r*_{z}).

The latter two may be made equal by a change of convention for the axes.

Three possibilities remain: (3D space + 1D time), (1D space + 3D time), or (2D space + 2D time).

An example of the third possibility would be a traveler who measured their horizontal angle relative to magnetic north and their vertical angle relative to the sun. Since magnetic north is (approximately) fixed, it serves to measure the horizontal angle spatially. Since the sun’s position continually changes, it serves to measure the vertical angle temporally. The result is (2+2) with (*r*, *θ*_{r}) and (*t*, *φ*_{t}).

Or one could do the opposite and measure the horizontal angle temporally, as with a sundial, and the vertical angle spatially, as with a theodolite. The result is (2+2) with (*t*, *θ*_{t}) and (*r*, *φ*_{r}).

If both angles are measured relative to a fixed point, then the result is (3+1) or (*t*, *r*, *θ*_{r}, *φ*_{r}). If both angles are measured relative to a moving point, then the result is (*r*, *t*, *θ*_{t}, *φ*_{t}). The moving point should be moving at a constant rate, or at least a constant acceleration.

If three coordinates are measured relative to a fixed axis, then the result is (1+3) or (*t*, *r*_{x}, *r*_{y}, *r*_{z}). If three coordinates are measured relative to a rotating axis, then the result is (*r*, *t*_{x}, *t*_{y}, *t*_{z}). The moving axis should be moving at a constant rate, or at least a constant acceleration.

The potential reality of (*r*, *t*, *θ*_{r}, *φ*_{r}, *θ*_{t}, *φ*_{t}) collapses to one of the possibilities above in the act of measurement. The potential reality of (*r*_{x}, *r*_{y}, *r*_{z}, *t*_{x}, *t*_{y}, *t*_{z}) collapses to one of the rectilinear possibilities above in the act of measurement.