This schematic figure illustrates the concept of radar distance between two Langevin observers in Minkowski spacetime. Langevin observers rotate rigidly around r = 0 (in a standard cylindrical chart) with angular velocity ω.

In the figure, a Langevin observer sends out a radar pulse at event A which hits another Langevin observer riding the same rotating ring at B′ which returns to the first observer at event A′;. To determine the radar distance, he divides the elapsed time (as measured by an ideal clock which he carries) by two.