  This conference centers on photoionized plasmas, and the tools necessary to
understand them. One of the major goals of meetings held between developers of
plasma codes is to identify sources of differences between various codes, and
resolve them. Very often these differences are caused by bugs. This
contribution outlines some practical aspects of developing bug-free codes, and
is based on my experience creating the plasma simulation code Cloudy.
  Computers present nothing less than a new way to understand the universe. We
can do any numerical experiment we can imagine. But machines are growing faster
far more quickly than people are getting smarter. Harnessing the power of
future machines in a reliable way will present an ever greater intellectual
challenge. More powerful machines allow a more complete and complex simulation
of physical processes, and so offers a far greater opportunity for errors.
Industrial standards of quality control, and the associated code development
techniques, can play a major role in developing reliable simulations.
