The medium-resolution wavelength range (L01) mode allowed for a grating range scan covering a wavelength range specified by the user up to the full range of 43-197 microns. The spectrum is composed of 10 sub-spectra with the sub-spectra being generated by the grating scanning over the 10 LWS detectors simultaneously. In practice this mode was almost always used for a range scan covering the entire LWS range. The spectral sampling allowed was 1, 1/2, 1/4 or 1/8 of a resolution element and the scanning speed was always such that only one ramp per sampling interval was taken, with signal-to-noise built up by taking more than one scan.
This Medium-Resolution Line Spectrum (L02) mode allowed for a grating range
scan of up to 
7 spectral elements around up to ten wavelengths specified
by the observer.
Data were recorded from all ten detectors
while the specified ranges are being scanned. The observer had the choice
of the spectral sampling interval, between 1, 1/2, 1/4
and 1/8 of a resolution element.
This mode was produced by specifying zero-width
scan in the medium-resolution line-spectrum AOT (L02).
By consequence the grating was not scanned but remained at a
fixed position. This produced an under-sampled medium-resolution spectrum
by providing ten photometric points -- one in each detector --
at 46.2 
m, 56.2 m, 66.1 m, 75.7 m, 84.8 m, 102.4
m, 141.8 m, 160.6 m and 178.0 m.
This AOT consisted in a Fabry-Pérot scan covering a wavelength range
specified by the user, up to the full range of the LWS
(46-196.7 m). Although the
wavelength range specified by the user covered only one detector, data were
recorded
for all detectors together. The observer had the choice
of the spectral sampling interval, between 1, 1/2, 1/4
and 1/8 of a resolution element.
Note that as a full spectral scan with the Fabry-Pérot took a very long
time, a significant part of
the spectrum has been recorded at high resolution (with L03)
only for four objects: Orion BN/KL, Sgr B2, Sgr A and Jupiter.
This AOT produced up to ten Fabry-Pérot scans over a small intervall around wavelengths specified by the observer. For each line the grating is fixed, hence all the data resides within one grating element. Although the grating position was optimised only for the wavelength of the specified line and hence for only one detector at a time (the prime detector), data is recorded from all detectors. The observer had the choice of the spectral sampling interval, between 1, 1/2, 1/4 and 1/8 of a resolution element.
When another instrument was the prime instrument, the LWS operated in parallel mode and when no AOT was active the LWS operated in a serendipity mode. This mainly refers to those times when ISO was slewing. The actual configuration of the LWS instrument for the parallel and serendipity modes is identical. These modes were not used until revolution 237 and continued until the end of the ISO mission with a gap between revolutions 380 and 442 when LWS was switched off due to a problem with the interchange wheel.
While not observing as prime instrument, some of the data in the LWS housekeeping was not necessary and the LWS parallel and serendipity modes were implemented by replacing this data with detector signal values calculated on board. The space available provided for two values from each detector to be placed in each telemetry format every two seconds. For this reason the instrument was not scanning but was used in the Narrow-Band Photometry mode (see Section 3.2.3 and the detector integration time on board was adjusted to provide 1 s integrations in these modes rather than the 1/2 or 1/4 s used during prime observations.