And S is, it's, you know, obviously, S doesn't really stand for position, but P, you know, it kind of looks like rho for density, and D we use for differentials, or distance, or displacement. So S is what gets used for position very often. So let's say S is our position. And let's see, this is T for time. T for time. And let's say this is in hours. And let's see, we care about the interval from time going from time one, time one, to time two, time two.