The effective time constant of a pitot tube can be determined by considering together the effect of lumping density changes and spatial variations in velocity. From lumped analysis the time constant is

for air flow. Thus the value of time constant for a pitot tube obtained from lumped analysis is a function of both the radius and the tube length.

Consider spatial variation next. The associated time constant is . The attenuation factor can be expressed as the reciprocal of the equivalent resistance, namely

Values of for each frequency can then be obtained from Table 2 using this formula. The optimum value of is determined using a least squares procedure through the reciprocal of the data in Table 2. This gives in dimensionless form and can be calculated for any value of .