Contents - Previous - Next Two procedures are commonly used for
determining flux rates. These have become known as the two-point
and multi-point methods. It may often be supposed that these
procedures are basically the same, the two-point procedure being
an abbreviated multi-point method. This is not, however, the
case for although the underlying assumptions outlined in Section
4.2 apply in each case, the two-point procedure is more tolerant
of deviations from the model than the multi-point method,
essentially because the two-point method measures total flux
between two points several days apart whereas the multi-point
method attempts to provide a mean value for daily flux rates
over the same time interval. 4.4.1 Two-point method If N remains
constant during an experimental period total outflow r' is
correctly calculated for a period between t1 and tt as: where
the subscripts refer to times 1 and t and pre-dose (p). This is
true even if the rate of outflow per unit time is not constant
and varies in a random