Hello all. While browsing Lorenz and Poincare Invariance - 100 Years of Relativity, I came across the followng:- -----The meter is the length of path traveled by light in vacuum during a time interval of 1/299,792,458 of a second----- This is, i believe, the generally accepted definition. Then the following-----As stressed by Leon Hsu, "The Principle of Relativity implies that the speed of light is a universal constant if and only if time is measured in units of meters"------ Two questions. Firstly: Is this a respectable source? It seems authoritative if perhaps somewhat unconventional in that other derivations of Relativity are discussed. Secondly: If the quote can be taken seriously why should it be the case that the units used for light speed matter? Thanks for any comments. Matheinste.