Gastester is used for the testing and setting of all petrol carburettor and injection systems on any vehicle. It provides a simple and inexpensive method of showing the correct air-fuel ratio. The procedure ensures settings are within the vehicle manufacturer's tolerance limits for C.O. content in exhaust gas. Calibrates in air, no moving parts to wear out, and no filters to change and is accurate to 0.5% C.O. measurement.