Count distinct in Pivot table Excel 2013

[LauraWork]

hi all

I have recently upgraded to excel 2013 from 2010 and I have set up some new pivot tables using the data model function so I can count distinct items.

However what I want to know is if I open a report created in 2010 can I then use the count distinct function? I can't seem to get it to work and I don't fully understand the 'data model' thing but can I not add it to existing pivot table?

thanks in advance