Ah, I see that in the manual now. No 10MHz reference input. Could be a fun project to add a better reference. They can often be had really cheap on eBay.
Still a useful instrument. I have been known to use two or three frequency counters at once to measure things like divide by N circuits, etc. I have some old Data Precision counters (almost as old as your Fluke, but I think they do ~100MHz) that I use as extra counters when I just need to check a few frequencies at once. Comes in handy.