yeah, but Mitsu uses an ultrasonic vortex detection system-
no kidding! They drag the air though a funky aluminum matrix to make it turbulent, then shoot sound waves through that to see how much of it there is.
And if that only makes a little sense, well, it's 'cause it only makes a limited amount to me! But Mitsu used it for quite a few years, on lotsa cars...

fwiw,
t

'89 V6 4dr- '4- Doris'