Crossword Genius

Ernst —, Austrian physicist who devised a system of speed measurement (4)

Ross

I believe the answer is:

mach

(Other definitions for mach that I've seen before include "Austrian physicist, gave name to speed no." , "Ratio of a body's speed to the speed of sound" , "Ratio of the speed of a moving body to the speed of sound" , "Ratio used to measure high speeds" , "-- Number relates to speeds" .)

I've seen this clue in The Mirror.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.