I was wondering if there was a way to create a function for the following. I am trying to update a cell, say G3 with a value in D3 but I want to do it on a certain date. I want for that cell to update on that date and then lock in with the value.

For example, if D3 has a value of 30, I want for my G3 cell to update with 30 on 10/12/2012. After that date I want that value to lock in as the data in D3 will change over time. This formula would need to be copied as I am trying to find a trend detail on a weekly basis.

Any help would be appreciated, thanks in advance!