A piezometer tube consists of a vertical tube that is open to atmospheric pressure at one end. A sphygmomanometer is a type of piezometer that is used to measure blood pressure. A force balance determines the height of the manometer fluid:
is the hydrostatic pressure of the manometer fluid,
is specific weight,
is specific gravity,
is the density of water,
is acceleration due to gravity, and
is fluid height.
In a simple U-tube manometer, fluid
can be a gas or a liquid. A force balance is used to calculate the fluid height:
is air, the specific weight is negligible, so the force balance simplifies to:
The advantage of using an inclined tube manometer is that slight changes in the pressure of the manometer fluid
give significant readings along the incline. For an inclined manometer open to atmospheric pressure at one end:
the vertical height of the fluid in terms of the length
is given by:
and the change in pressures is:
If the inclined manometer is closed at both ends:
View the screencast video  for an example problem using this type of inclined manometer.
The screencast video  shows another worked example problem.
 B. R. Munson, T. H. Okiishi and W. W. Huebsch, Fundamentals of Fluid Mechanics
, 6th ed., Hoboken, NJ: John Wiley & Sons, 2009.