OMRON NT31C alarm history

I set up an alarm list and corresponding alarm history screen for my customer. All alarms in the list are check marked in the table to be part of the history. We shipped the machine in Feb. and everything seemed fine. I went on a service call this week for something else and we discovered that the history screen has not recorded anything since late Feb. I can't find the answer to this in the screen manual except maybe that there is a limit of 250 messages. If the history has a limit how do I set it up to remember the most recent ones, etc? Thanks for any advice.

You need to check the box for "Use Ring Buffer(FIFO) in System Tab.

aha! Thanks. I've got 5 machines to fix