ExcelBanter - Question regarding Excel functions

Greetings,

I am trying to create a schedule of values for work. On this schedule,
I want to track hours used in three columns: 1) past used, 2) current
usage, and 3) total used. Past will olny be calculated when a new
number is inputed into "Current Usage." So, for example, in the first
bill period, current usage is 25 hours. So, by putting 25 hours in
column 2, column 3 is also updated to 25 hours. In the second billing
period, current usage is 30 hours. When 30 hours is put into column 2,
column 1 becomes 25 (from previous period) and column 3 becomes 55
hours. I got this to generally work with a simple IF function in
column 1 that looks like this: =IF((C2-B2)<0,0,C2), this worked great.
However, here is where my question/problem arises. If I start making
another row to track hours for something else, columns 1 and 3 of my
initial tracking keeps updating. Even if I am working on something in
another excel file, if I enter something and hit "enter," or hit
"delete," my initial functions for columns 1 and 3 keep updating. I
cannot seem to figure this out. Please help me.

Benkyo

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benkyo11
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