  We report on measurements on a sample consisting of two nominally identical
single-electron transistors the islands of which are coupled capacitively. One
transistor at a time is operated as electron box. The remaining transistor is
used as an electrometer to measure the charge on the box island. While ramping
up the box gate voltage transitions occur periodically between states which
differ in the charge on the box island by the elementary charge. This shows up
in jumps of the electrometer current. The coupling between the box and the
measuring device causes a broadening of the transition width not included in
the formulae for an isolated box. This is evident in our data as well as from a
thorough analysis of the system in the framework of the sequential tunneling
model.
