Convert Sum value to text

Hello!

Trying to convert a sum value to appear as text.

Here is my formula:

if Sum ({@Thurs Daily Count})=0 then 0 else

Sum ({@Thurs Daily Count},{PTS_1_18_13_10_09.Scheduler}) / Sum ({@Thurs Daily Count})*100

I want to have this appear as "NA" instead of appearing as 0.  I believe I'll need to convert the number 0 to text "NA".....?  Thanks!

Rich