(make-chronometer)
Returns a new chronometer object.
(chronometer-start! <chronometer>)
(chronometer-stop! <chronometer>)
(chronometer-reset! <chronometer>)
resets <chronometer> time to zero.
(chronometer-accuracy <chronometer>) ;; optional
(chronometer-time <chronometer>)
measures the elapsed accumulated time between the starting times and stop times.