Later addition of fermentables

The recipe that I have calls for me to add 1 lbs of sugar a week after fermentation starts.  Any ideas on how to combine the gravity reading of my beer before fermentation and the gravity reading of this 1 lbs of sugar in order to get a more accurate "Actual Gravity" reading?

Hi,
  I would mark the sugar as "Add after boil".  Since the sugar is 100% soluable in the wort, the estimates should be very accurate.  If you want a good pre-sugar estimate, just delete the sugar, note the OG and then add it back in.

Cheers,
Brad

Thanks.

If I measure my OG right before pitching yeast and then a week later I measure the gravity of the 1 lbs of sugar in the pint of water, do you know of an equation that would tell me how to combine those numbers for a "total" OG?  That way, when I measure the FG, BeerSmith will calculate the right alcohol percentage.