Combined calibration gases include combinations of different gases that are used to calibrate measuring instruments. These gases are usually prepared in precise and specific ranges of concentration and are used for the calibration of various measuring instruments, including gas sensors, gas analyzers, pressure and temperature measuring instruments, etc. Combined calibration gases usually include oxygen, nitrogen, carbon dioxide, and other gases such as propane, butane, methane, etc. These gases are prepared and produced in a controlled environment to provide more accuracy in the calibration of measuring instruments.