public void updateAccelerationSeries(Step step, long timestamp) {
   accelerationSeries.addOrUpdate(
       new TimeSeriesDataItem(new FixedMillisecond(timestamp), step.getClusterId()));
 }
 public void updateVelocitySeries(Step step, long timestamp) {
   velocitySeries.addOrUpdate(
       new TimeSeriesDataItem(new FixedMillisecond(timestamp), step.getClusterId()));
 }