  By observing bright and compact astronomical sources while also taking data
with the 183 GHz Water Vapour Radiometers, ALMA will be able to measure the
`empirical' relationship between fluctuations in the phase of the astronomical
signal and the fluctuations of sky brightness around 183 GHz. Simulations of
such measurements assuming only thermal noise in the astronomical and WVR
receivers are presented and it is shown that accurate determination of the
empirical relationship should be possible in a relatively short time. It is
then proposed that the best way of using these empirical coefficients is to
include them as a constraint on a physical model of the atmosphere -- this
allows them to be used for longer period of time, increasing the efficiency of
observing. This approach fits naturally into the analysis framework presented
in the previous memo, which has now been extended to implement it. The
technique is illustrated via simulations and on a short data set collected at
the SMA.
