In a number of threads over the years the idea has been discussed that if odometers were as well defined as (and as nearly realizable) as clocks, arguments we sometimes get that distance/length contraction 'disappears' when you stop, so it is meaningless, would have less weight. Now, nothing can get around the fact that given manifold with metric, proper time interval is defined along any arbitrary world line, while something more is needed for any concept of an odometer. The minimal extra thing needed to imagine any world line as having an odometer as well as clock is congruence of reference world lines, which would normally be desired to be some flavor of co-moving congruence (but this is not necessary). Then, the congruence defines an imaginary, space filling history of reference markers. We have no interest in their separation with respect to any foliation - my proposal needs only the congruence, not a foliation. Then, the motivating concept is that a traveler can watch markers go by, unrolling imaginary tape measure matching the speed of markers as they go by. Then distance traveled for any path with respect to the markers is the amount of tape unrolled. Putting this into a formula is easy. At any moment along a curve parametrized by tau, you have the orthonormal local frame or tretrad defined by the 4 -velocity (really, many of them, but it won't matter which you choose). In this frame, the congruence world line at this event has some speed (we don't care about direction, which is why we don't care about which orthonormal frame you choose at any point of the travel world line). The odometer reading is defined as: ∫v([itex]\tau[/itex]) d[itex]\tau[/itex] Then, when a traveler reaches some destination, they see that local clocks have advanced far more than their clocks, but they know that their path through spacetime elapsed less time, and this is a characteristic of their path. Similarly, when they stop, they see that observations by local astronomers say they traveled a long distance, but their odometer, characterizing travel relative to regional markers, is much less, and this is also a function of their path (for a given family of markers). In general, the higher the average v for a path, between two chosen world lines of the congruence, the lower the proper time and the shorter the distance traveled. But, for any average v << c, the distance is essentially constant (while proper time = ∫ d[itex]\tau[/itex] obviously grows without bound as average v decreases). Opinions on value, pitfalls, or any other responses?