Custom formula returning "NaN" and doc won't save. Help!

Custom formula returning "NaN" and doc won't save. Help!

I created a simple custom formula that operates like: column1 / column2. The data in column 2 is occasionally 0 (it's click data from a PPC campaign and some days there are zero click on a particular ad) but this prevents me from saving my report because it reads as an error.

Can someone please help me solve this issue? How can I tell Zoho to discard 0s when using this formula?