level, shut off the water supply and allow the water level to fall
to 80 mm (3.2 in.). At this point, start the stop watch and
determine the time for the water level to fall to the 20-mm
(4⁄5-in.) level. Record the inside diameter (d) of the upper unit,
the diameter (D) of the exposed portion of the specimen, and
the water temperature (T). Make at least five readings per
specimen. All measurements in 13.3 are in relation to the outlet
water.