  SCUBA-2 is a 10000-bolometer submillimetre camera on the James Clerk Maxwell
Telescope (JCMT). The instrument commissioning was completed in September 2011,
and full science operations began in October 2011. To harness the full
potential of this powerful new astronomical tool, the instrument calibration
must be accurate and well understood. To this end, the algorithms for
calculating the line-of-sight opacity have been improved, and the derived
atmospheric extinction relationships at both wavebands of the SCUBA-2
instrument are presented. The results from over 500 primary and secondary
calibrator observations have allowed accurate determination of the flux
conversion factors (FCF) for the 850 and 450 micron arrays. Descriptions of the
instrument beam-shape and photometry methods are presented. The calibration
factors are well determined, with relative calibration accuracy better than 5
per cent at 850 microns and 10 per cent at 450 microns, reflecting the success
of the derived opacity relations as well as the stability of the performance of
the instrument over several months. The sample-size of the calibration
observations and accurate FCFs have allowed the determination of the 850 and
450 micron fluxes of several well-known submillimetre sources, and these
results are compared with previous measurements from SCUBA.
