"Old Nick" wrote: (clip)I _believe that if the air bubble occurs _and the
water levels are already exactly equal, and you don't alter anything_ then
you are OK. Any change with an air bubble and you will get wrong readings.
^^^^^^^^^^^^^
The water hose is essentially a U-tube, in which the water levels are
PRESUMED to be at the same level in both legs. Obviously, if there is air
on one side, the weight of water required to match the other leg will stand
higher in that leg, introducing an error. The best way to make sure this
doesn't happen is to bring both legs together and see that the levels match.
To be doubly sure, raise the ends of the hose, so any air rises and escapes.
Once this is done, there is no way for air to get in, and the system should
be accurate, no matter how you drag the hose, or whether it goes over bumps
or low spots.