Hi everyone,
I'm trying to create an inventory sheet where i have a correct record of
goods available for sale.

What i want is to be able to overwrite figures in a particular column and
have that added to figures in another column. For example. Say i have 25 Cds
and i sold 10, i now have 15 availible for sale. However, if i bought 50
more, i should now have 65. Is there a way i can write the figure bought in a
cell and have that added to the figure in the existing stock?

Also, each time stock for a particular product is bought it is recorded in
the same cell, ie. the old figure is overwritten, so the 25 is replaced with
50.
Thanks.