  Calibration means that forecasts and average realized frequencies are close.
We develop the concept of forecast hedging, which consists of choosing the
forecasts so as to guarantee that the expected track record can only improve.
This yields all the calibration results by the same simple basic argument while
differentiating between them by the forecast-hedging tools used: deterministic
and fixed point based versus stochastic and minimax based. Additional
contributions are an improved definition of continuous calibration, ensuing
game dynamics that yield Nash equilibria in the long run, and a new calibrated
forecasting procedure for binary events that is simpler than all known such
procedures.
