Hi Philo
I can concur that it works perfectly with a computer as it did for me years
ago on my Mini Cooper - about every 500 miles - those twin SU carbs were
always getting unbalanced - well they did, due to the way I drive the car
I still have that piece of tube(rubber hose) given to me by a garage that
specialised in 'car tuning') - 6" long a 1 inch in diameter - or a cardboard
insert from a roll of kitchen paper - but the sonic effect is not as good as
the rubber tube.
I used it recently to detect a faulty fan in a power unit.
One of the twin 80mm fans bearings had gone - got it swapped free of charge
with a single 120mm fanned unit.
Rgds
Antioch