conditional formatting

Hi all
Just wondering if you could help with a query. I have a fairly large spreadsheet using around 2500 rows and 30 or so columns. I have some conditional formatting that I want to clean up. One column in particular is formatted to highlight duplicate data. I now have dozens of these rules in that column from where I insert new rows and the format copies, but that is ok I understand that happens. I have noticed though that there are also dozens of other 'n/a' rules that I didn't put in and I wonder what they are for and is it safe to delete them? In the C/F Rules Manager box the rules are listed as below:

Rule Applies To
Duplicate Values =$B$1485:$B$1486
Cell value = "n/a" =$B$1485:$B$1486
Cell value = "n/a" =$B$1485:$B$1486


any ideas on this?

thanks
Steve

Thank you
i have gone through and deleted all of them - right across several of the columns. There were a lot more than i thought there would be, as well as several other conditional formats that had mysteriously appeared in columns where they shouldnt have been. I dont know how they got there but hopefully I now have them all removed for good. It seems to have done the trick though as it now seems to work much more speedily