Geothermometric and geobarometric methods are considered under two groupings: directly calibrated methods and internally consistent data set methods. Emphasis is placed on the importance of error propagation calculations. They allow the calculation of model uncertainties on temperatures and pressures due to the quantifiable uncertainties involved in the calibration and application of methods. The possibility of systematic errors, due to the unquantifiable effects of the assumptions and approximations involved, must be evaluated using the criterion of geological reasonableness.
The advantages of the internally consistent data set approach are expounded and an appropriate error propagation procedure developed.