  Procedures and results on hardware level detector calibration in
Super-Kamiokande (SK) are presented in this paper. In particular, we report
improvements made in our calibration methods for the experimental phase IV in
which new readout electronics have been operating since 2008. The topics are
separated into two parts. The first part describes the determination of
constants needed to interpret the digitized output of our electronics so that
we can obtain physical numbers such as photon counts and their arrival times
for each photomultiplier tube (PMT). In this context, we developed an in-situ
procedure to determine high-voltage settings for PMTs in large detectors like
SK, as well as a new method for measuring PMT quantum efficiency and gain in
such a detector. The second part describes the modeling of the detector in our
Monte Carlo simulation, including in particular the optical properties of its
water target and their variability over time. Detailed studies on the water
quality are also presented. As a result of this work, we achieved a precision
sufficient for physics analysis over a wide energy range (from a few MeV to
above a TeV). For example, the charge determination was understood at the 1%
level, and the timing resolution was 2.1 nsec at the one-photoelectron charge
level and 0.5 nsec at the 100-photoelectron charge level.
