I am having a hard time trying to figure out a solution to this problem.  I
am setting up a spread sheet with shipping weights.  Some packages go out
over weight other go out under weight and I want to setup a spread sheet that
shows the total weights we are off.  I have a colom that has our weight, the
next colom is the shipper's weight, and the 3 is how much the weight is off.  
The probem that I have is that with the weights in the 3rd row when I add
them up I have postive and negative numbers so I am not getting a true total
off the how much we were off by in our systems.  I am wondering how can I
make this so that negative numbers will add up as a postive number or that a
negative number will show and add up as a positive number.  

Thanks