ok, the pendantic nerd in me has to point out that replacing stored X, Y state with data from the system is NOT eliminating state.
It's just changing who is responsible for managing the state. The gradually increasing Time constant is still state, and it's still got code storing it, and gradually increasing it. This is _exactly_ the same thing as storing and changing X, Y coordinates, you've just outsourced the work and created code that's dependent upon the side-effect of an external system.
If we want to get really pedantic it's also adding a dependency, but if you can't trust the system clock you've got bigger problems than having an additional dependency. ;)
It's just changing who is responsible for managing the state. The gradually increasing Time constant is still state, and it's still got code storing it, and gradually increasing it. This is _exactly_ the same thing as storing and changing X, Y coordinates, you've just outsourced the work and created code that's dependent upon the side-effect of an external system.
If we want to get really pedantic it's also adding a dependency, but if you can't trust the system clock you've got bigger problems than having an additional dependency. ;)