How can I access the sum of another table in a formula in another table?

Make sure that every record in table #1 is linked to table #2. That could be anything. A month, a week or any random number. As long as all records are related to that specific single record in table #2.

Then, in table #2, create a ROLLUP field. In that ROLLUP field you will be asked which field you want to roll up. Pick the specific field in table #1 with the amount you would like to sum.

In the last box in your ROLLUP field, choose SUM(values) and voila.

Thanks Andre,
I figured it out. In my case, what I needed to do was create a calc table that contains only one record, and link it to every record in table A. Then, I was able to get a rollup of every record in the table B into one cell. Then I was able to reference that from table A, where I needed the number to perform the calculation. It’s clunky, but it works.