Budget, bids and pause rules can be set based on custom math expressions.
Math expressions are used to define custom calculations and columns in reporting. We find expressions useful to pass in your custom data that you are not passing into the Facebook SDK or mobile measurement partner. This allows you to import in-app events or offline events and see the data in AdRules mapped to your Ad Set’s targeting.
Setting Custom Expressions
From the Advanced Reporting Tab, click on the Settings icon, then click on Expressions.
Here, custom expressions can be defined by adding, subtracting, multiplying or dividing two data columns.
For information about setting manual rules based on expressions or ROAS,