Sum question/problem in c#

Question

Hello,

bellow you can see 2 programs, that on right side is the original program and that on the left side is program developed by me..
the original program still works, but the developer stopped to update it.. that's why i try to create a new one.



well,problem is that I don't know how to cumulate some values
for example see on the right side on MCB-25: 920, and on left side 240 if i click on my program button start and another value comes at MCB-25: it replaces the old one, i want to cumulate those values.


attached is the code of this form..


thank you.