freeze calculations in Numbers

I'm tracking some stocks that I have in numbers and have it set up to calculate the values based on the price, which is automatically updated nightly.

At the end of the month, I'd like to "freeze" the calculations for that month, and re-calculate for the new month.

So is there way to "freeze" (and that's probably the wrong term...) calculations, so they don't change values any more.

So on Jan 31, I can "freeze" the calculations for January, and setup a new column for February based on the calculations...