Capacitive systems are often set up by firstly measuring the volume of fuel in the tanks with a dip stick. Hydrometers are used to measure density and the mass is calculated. The system is therefore only as accurate as the initial measurement using the dip-sticks. My experience is that this is where most mistakes are made. Often the SG is made up, as a hydrometer is not used.
The ultrasonic system is much less reliant on the human element in this respect. The bubbles are a problem for both systems, but software tunes out the effect in ultrasonics.
1% accuracy is impossible. fuel itself varies too much for that. 3% is more realistic for a modern system.