The temperature stability of the well and response time depend on the width of
the proportional band. If the band is too wide the well temperature will deviate
excessively from the set-point due to varying external conditions. This is because
the power output changes very little with temperature and the controller cannot
respond very well to changing conditions or noise in the system. If the
proportional band is too narrow the temperature may swing back and forth
because the controller overreacts to temperature variations. For best control
stability the proportional band must be set for the optimum width.