In pure math, the derivation is not this ratio d(s)/d(t) (t) for a specific choice of dt (=0.001). Instead, it's whatever that ratio approaches, as your choice for dt approaches 0.
In pure math, the derivation is not this ratio d(s)/d(t) (t) for a specific choice of dt (=0.001). Instead, it's whatever that ratio approaches, as your choice for dt approaches 0.