Comparison of Variances

I have individual workbooks that contain amounts for a specific month. I’m wondering if there is a formula and/or function that will show the difference (positive or negative) between two months or a range of months. My aim is to analyze and compare the variances.

As an example, the attachment is the template where the variable amounts are inputted for a specific month. For example, I want to see the Volume (or Unit Price, Service Charges, etc.) difference between Month 1 and Month 2 for each sub-item in Column A, starting with ACCOUNT MAINTENANCE – MONTHLY.

Thank you in advance if someone can provide assistance, or direct me to an existing thread that answers this question.