After the liquid helium depletion of ISO, an engineering test programme was conducted on the different satellite systems. Besides functional tests of the various redundant systems, a lot of time was devoted to the testing of alternative pointing strategies in case of failure of one or more gyros.
During this test programme the temperature of the focal plane remained low
enough to operate the InSb band 1 detectors of the SWS. The instrument
could be operated in some timeslots available during the engineering
test programme. This time was used to record spectra of stars between
2.36 and 4.05 
m at medium resolution (
1500 - 2000).
As the temperatures of the focal plane increased, changes in the position
readout of the grating scanner and changes in the response of the
instrument could be seen. In this chapter, the observation
mode and the calibration of the changing characteristics of the instrument is
presented.