Alnor 9870, Owner'S Manual, Page: 16 / 21

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APPENDIX A
Standard Velocity vs. Actual Velocity
Since thermal sensors are sensitive to changes in air
density and air velocity, all thermal anemometers
indicate velocities with reference to a set of
standard conditions. For Alnor instruments,
standard conditions are defined as 70°F (21.1°C)
and 14.7 psia (101.4 kPa). Other manufacturers
may use different values.
Standard velocity is the velocity the air would be
moving if the temperature and pressure were at
standard conditions. It is usually the most useful
measure of airflow because it defines the heat-
carrying capacity of the air.
Actual velocity is the velocity at which a micro-
scopic particle of dust would be traveling if it were
in the air stream.
Because actual air density is rarely equal to air
density at standard conditions, actual velocity
usually differs from standard velocity.
In some instances, actual air velocity rather than
standard velocity may be of interest. To obtain the
value for actual velocity, multiply your standard