Stellar parallax remains the standard for calibrating other measurement methods. Stellar parallax remains the standard for calibrating other measurement methods (see Cosmic distance ladder). Scale of temperature is a methodology of calibrating the physical quantity temperature in metrology. Theoretically based temperature scales are used to provide calibrating standards for practical empirically based thermometers. Most velocity-based meters have an adjustment vane for calibrating the meter to the required accuracy. But such master gauges are still important for calibrating and certifying metrological equipment. This contained buildings for testing materials, preparing uranium, and assembling and calibrating instrumentation. Various researchers have investigated the use of saturated salt solutions for calibrating hygrometers. Point sources are used as a means of calibrating ionizing radiation instruments. Accuracy can be improved by calibrating the dichromate solution against a blank. In teaching laboratories, benzoic acid is a common standard for calibrating a bomb calorimeter. The primary technique for calibrating the ages to the Common Era calendar is radiometric dating. HMDSO is used as an internal standard for calibrating chemical shift inH NMR spectroscopy. This is useful in calibrating instruments and designing aircraft. Interferometry has been used in defining and calibrating length standards.