Running total in a single cell

[rd_CEM]

I want to be able to have a running total in one cell. I've searched online and the closest I've found was the formula in the attached pic. This is for defect calculation. Say I have 30 boards I'd like to be able to just type a number into the cell and have it add to what is already there. Ex. 5+10 defects from the next board will add to 15. The formula shown (unless I read it wrong) should keep a running total in column F by adding the number entered into column E. Hope this makes sense. Appreciate any help. TIA

 

[Micron]

I'd like to be able to just type a number into the cell

You have a 5 somewhere and you want to change that to an 8 and have it add 8 to the value in some other cell? I can only think this is possible via vba code, but I could be wrong. Why are the values not in a column that you just sum, like =Sum(D:D)?

Your formula can only return True or False (0 or -1), and such will only ever be False. It says F3 (which can only be 0 or -1) equals (5 = 0) or
says F3 equals (5 = -1)
5 can never equal 0 or -1