Premium is so you can store all your logs and we can see the history too.
In either poolmath, go into the upper left menu and select 'effects of adding' fill in your gallons and select SWG.
Then select your SWG from the list, 'calculate for free chlorine' and fill in the hours and %. It will tell you the expected production at the bottom.
You can also change calculate for FC to run time or % to do it the other ways. Basically you give it 2 of the 3 and it calculates the 3rd.