  We describe the conditional and unconditional dynamics of two coupled quantum
dots when one dot is subjected to a measurement of its occupation number using
a single electron transistor (SET). The measurement is made when the bare
tunneling rate though the SET is changed by the occupation number of one of the
dots. We show that there is a difference between the time scale for the
measurement-induced decoherence between the localized states of the dots and
the time scale on which the system becomes localized due to the measurement. A
comparison between theory and current experiments is made.
