The other method is called interferometry. Interferometry relies on the nature of light to travel in waves. Wavelengths of photons interfere with each other making crests or troughs much like waves in water do. The wave pattern of two beams of laser light hitting each other tells you about the difference in distance the two light beams had to travel. Interferometry can measure very small distances, around the size a wavelength of light.

Interferometry is used in industry to make highly accurate measurements of the size of tiny, delicate instrument parts. It was also important historically with Einstein's formulation of the Theory of Relativity.