E30 Question

Pic for attention. Good morning y'all, i bought all needed to jump into E30 but i was guessing how do you all know the porcentage of gas in your tank? I have a COBB accesport but i can't find an option on the gauges that meassures that in particular. Maybe is not available on COBB? If not how you E30 people does the mix? Thanks in advance!

https://preview.redd.it/ihkyds50h91e1.jpg?width=6000&format=pjpg&auto=webp&s=f23880d9deb19327649c224a71fffd89069481bd