If you're managing your line items manually, you may run into scenarios where you need to do a bit of math. For example, maybe you're not interested in line-by-line granularity. Maybe you want to group a few lines together and use one category for those and then group a few more lines into another category.
Perhaps you have some specific tax rate calculations you'd like to perform when setting the line item tax amount.

These are good cases for performing inline arithmetic directly in the Total and Tax (if applicable in your country) line item fields.

Take a look at the below screenshot for an example of how to do this without deferring to a calculator or running these numbers in your head:

But it goes beyond the simple addition illustrated above. These fields support addition, subtraction, multiplication and division. If things get a little complicated, don't forget to use parentheses to set the order of operations. e.g.:
12.99 + (3.99 * 3) - (0.99*2)
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