Graphite Sync knows when to expect the next value in graphite and polls *just-that-value* appending it to the dataset, removing the oldest value, and calls your callback with the updated data and date range.

graphite_sync.coffee

# initialize graphite syncr
g = graphite_syncr {url: "/graphite/render?target=...",
                    inteval: 3000, #optional
                    callback: (data, sdate, edate) ->
                        update_plot(data) # calls with full dataset
                        dr(sdate,edate) # optional arguments sdate & edate
                        window.history.replaceState("",
                          "#{sdate} to #{edate}",
                          "/static/sog/iono/index.html?sdate="
                          + sdate.toISOString().slice(0,16) #2013-05-01T05:00
                          + "&edate="
                          + edate.toISOString().slice(0,16))
                    }

# Methods
g.pause()
g.resume()
g.status() == {state: "paused" ? "polling"
               next_poll: 213 #ms
               url: "/graphite/render?target=..."
               interval: 3000
               callbak: <function blah blah>

               #last_url, next_url, sdate, edate, last_polled
              }
g.t_minus() == 213 # 213ms until next polling