Most thermal analysis experiments are conducted under ambient pressure conditions using isothermal or temperature time rate of change conditions where time or temperature is the independent parameter. Some experiments, however, are conducted under reduced or elevated pressure conditions where pressure is an independent experimental parameter (Test Method E537). Oxidation Induction Times (Test Methods D5483, D5885, D6186, and E1858), Oxidation Onset Temperature (Test Method E2009), and the Vapor Pressure (Test Method E1782) are other examples of experiments conducted under elevated or reduced pressure (vacuum) conditions. Since in these cases pressure is an independent variable, the measurement system for this parameter shall be calibrated to ensure interlaboratory reproducibility.

The dependence of experimental results on pressure is usually logarithmic rather than linear.