In an online environment you often want to have the last N events inside a buffer, so that the experiment can be monitored continuously. To make it easier to handle this case, you can use routine HFNOV, which fills a circular buffer in memory with RWN events, and when the buffer is full, overwrites the oldest Ntuple.
Action: Fills a circular buffer with RWNs.
NVAR containing
the values for the current event.