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The Solar Backscattered Ultraviolet model 2 (SBUV/2) instrument on the National Oceanic and Atmospheric Administration (NOAA-11) satellite has measured global total ozone and its altitude profile in the stratosphere since 1989. For the ozone measurement, its monochromator scans 12 discrete wavelengths from 252-340 nm. An onboard calibration system malfunctioned in late 1994. This necessitated the development of alternative methods of characterizing sensor sensitivity change. Assuming that the seasonal variation of surface reflectivity is the same from year to year, we used radiance measurements at 340 nm over the polar snow and ice to determine long-term instrument sensitivity drift at 340 nm. The spectral dependence of sensor sensitivity change in 1993 was used as an initial estimate for the current calibration. We then refined the calibration at 313, 318 and 331 nm for the total ozone retrieval, using the D-pair validation analysis. The estimated uncertainty in the extended calibration is less than 1%. The updated calibration has been used for NOAA-11 SBUV/2 operation. The resulting NOAA-11 SBUV/2 total ozone data were compared with ozone data from the Earth Probe Total Ozone Mapping Spectrometers (TOMS). The two agree with each other to better than 2%.