  Weyl elaborated this idea by suggesting that the dynamical nature of such time keeping systems was such that they continually adapt to the spacetime structure in such a way that their rates remain constant. He distinguished between quantities that remain constant as a consequence of such dynamical adjustment, and quantities that remain constant by persistence because they are isolated and undisturbed. He argued that all quantities that maintain a perfect constancy probably do so as a result of dynamical adjustment. Weyl (1921a, 261) expressed these ideas in the following way: 