Progressivew subtracting of cells

[TravelingMan]

I have 3 columns.. In one column sales.. in the 2nd column Sales Target, in a third column.. sales difference

I want to add whereever there is a positive outcome with any negative before i.e

sales target Sales difference
100,000 80,000 20,000
200,000 250,000 -50,000
150,000 150,000 0
175,000 200,000 -25,000
100,000 150,000 -50,000
200,000 200,000 0
100,000 100,000 0
100,000 175,000 -50,000------ this comes from the difference in (175,000-100,000) (75,000) and and the accumulation of negative amounts before any other positive amounts (-125,000)
150,000 100000 0 (50,000-50,000)

so basicall needing a running totaL until a positive amount comes up.

Please let me know if this doesnt make sense.

 

[TravelingMan]

this may be a better explanation of what I am looking for

I have a commission sheet set up however, it takes into consideration the draw and percentage given based on sales.

my problem is being able to add (-) numbers to positive numbers anywhere in the doc

total for period (if negative, it will be added to the next positive period)

0
0
25,000
-10,000
0
0
25,000 (here this cell would be 25,000+(-)10,000) or 15,000
10,000
0
0
-5,000
-10,000
0
0
50,000 (would be 50,000 + (-) 15,000) or 35,000