Calibration refers to the process of determining the relation between the output (or response) of a measuring instrument and the value of the input quantity or attribute, a measurement standard. In non-specialized use, calibration is often regarded as including the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy. For example, a thermometer could be calibrated so the error of indication or the correction is determined, and adjusted (e.g. via calibration constants) so that it shows the true temperature in Celsius at specific points on the scale. Calibration also can refer to judgments made by a prognosticator, for example, a weather-forecaster who states that "there is an 80% chance of rain today," if properly calibrated, will say this on precisely 80% of the days during which it rains.