What diameter d must a 1.5-m-long pipe have so
that it has a conductance of about C = 1000 l / sec in the
region of molecular flow? The points l = 1.5 m and
C = 1000 l/sec are joined by a straight line which is extended
to intersect the scale for the diameter d. The value d = 24 cm
is obtained. The input conductance of the tube, which depends
on the ratio d / l and must not be neglected in the case of
short tubes, is taken into account by means of a correction
factor α. For d / l < 0.1, α can be set equal to 1. In our example