I'm using the HC-SR04 ultrasound device.
After reviewing the driver code, I believe there might be a bug.
I'm not sure of the scope this Driver was written for but it appears the cylinder volume is 2x larger then it should be. For Line 60 the string " * 2 " should be removed.
This is volume attribute is the same one displayed on the Hubitat Devices screen.
Where did you get the driver? Since you have the code, it's not built-in. Contacting the author would be the best hope to have it addressed at the source. Usually authors have a topic (thread) in the forum to discuss their releases, so that would be a good place to start. If you found it on Hubitat Package Manager or elsewhere, there should be a way to find it still.
Of course, you're also just free to modify it for your personal use, assuming there are no license issues with that.