To retain the value of previous record

Hi,

I have a worksheet which is use to calculate the work progress. The sheet will be update monthly. I have a column which record the contract hours for a job, then a column a Job to date hours, which is the job done till end of teh month, and then there a calculation to determine how many % of work have done for the month.

My problem is that i don't have the visibility of previous month % after the worksheet is updated. I wonder if there is any function in excel that can use to copy the previous cell value?


E.g.
Contract Hour JTD Hour Percentage
15 5 25%
20 20 100%

Total percentage 75%

Previous month percentage ?????

How do get the value for the previous month percentage? I certainly cannot copy directly for the total %. It'll be tedious to copy manually also as i have about 20 sheets of this for each different job.