public Datapoint getVisibleFirstDatapointLocking() {
Datapoint first = null;
waitForLock();
for (int i = 0; i < mSeries.size(); i++) {
TimeSeries ts = mSeries.get(i);
if (ts != null && ts.isEnabled() == true) {
Datapoint d = ts.getFirstVisible();
if (first == null) first = d;
else if (d.mMillis < first.mMillis) first = d;
}
}
unlock();
return first;
}
