This chapter discusses the expected accuracy of the data obtained by SWS, the products derived from them and indicates where the main sources of error lie. It is based on the SWS Calibration papers ``The Photometric Calibration of the ISO Short Wavelength Spectrometer'', by S.G. Schaeidt et al, ``The Wavelength Calibration and Resolution of the Short Wavelength Spectrometer'' by E. Valentijn et al and the general paper on SWS by de Graauw et al in the A&A special issue (November 1996 Vol 315) devoted to ISO.