keep previous formulas in tack
 

I have a spreadsheet that I used monthly addind info every month to the
existing file. I have link the subtotal row above link to the botton of the
spreadsheet. I need to keep last month inf. @ the bottom .The rows above
info. will change monthly . Once I enter new infor above the previour month
info changes. How do I keep last month's info in tack & still sue the
formulas.

e.g last month row Cell A1= 2, Cell A2 = 2, subtotal is Cell A3 = 4
I will enter A3 info. in cell (eg.) a10 = 4
I still need to keep the info in a10 for this month, I insert row A11 & copy
the formula from a10 to save time, however the info in a1 & a2 for this this
month will change. what I find is once the new info in entered in a1 & a2,
cell a10 changes.
How do I keep a10 from changing....

thx.
KIm