When looking to combine a variety of metrics you might wish to build your own formula that takes metrics into consideration from various different channels. Or if you happen to have a particular formula that you have in mind for a single channel you can also make that work.
We need to click on any widget and next to the channel you are using there will be three dots that you can hover over and click on 'create custom formula'.
Once you make that selection a formula builder interface will pop up:
Here you have full control of what channels or metrics you want to be using. You can multiply or divide metrics as well as put them into brackets for more complex equations. Just don't forget to give it a name at the top, specify the value type and outline positive or negative increase.
Once that is all set click on 'create custom formula' to see it in action.