How to measure and display liquid in a vessel?

[ClydeCrashKop]

I saw this capacitive liquid level gage on a boat today.
It uses 2 aluminum foil strips on the outside of a non-metallic tank.
This subject comes up often so I am posting it in the most recent thread.
https://www.tankedge.com/
Tank-Edge is a part of **broken link removed**. **broken link removed** is an industry leader in capacitive sensing technology with over twenty years development experience. Our liquid level monitors designed for the Marine and RV manufacturers and aftermarket installers provide years of service for non-invasive applications. Please view our products to learn more.
The iSeries is the only tank monitor tested and approved by the United States Coast Guard. It has patented technology with Level Alert™ and is NMMA Certified using ABYC standards. Other tank probes often become corroded or clogged with materials. This send false signals to the panel. Sensors on the iSeries system mount externally and actually read through the tank wall.

 

[hyedenny]

How about a tube the length of the vessel, open at the bottom end, and at the top end a gas pressure sensor. The tube would be calibrated by measuring ambient pressure with the vessel empty, then max pressure with the vessel filled. The volume in between would be linearly sensing the air pressure inside the tube as the liquid level goes down which is easily converted to liquid volume.
Simple hardware, simple software, and accurate.

Here's some sensors: https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25