Excel sheet

We have an excel sheet that we need formulating. The current formulas on the sheet are not calculating correctly.
The sheet is currently showing modules in and modules out. The modules out should be showing as a negative on the module count but its showing as plus which means our future totals are showing alot higher than they should be.
We also need the excel sheet to be broken down into Months per tab so we can see a monthly view but we want the formulas to be on each tab/month. Currently the sheet starts from Feb 1st all the way through to current date. We need to hav each month on there own tab we end totals.