Through the glass insulator of the Colortune you can see the combustion flame. Its colour indicates what the fuel-air-mixture is like. This way you can adjust your engine / carburettor. Rich mixture --> Orange or Red flamecorrect mixture--> blueish, yellow flameLean mixture--> blue or white flameThe video is just to show the principle, to really perform a setup it s neccessary to do that under load (on the road or safer on a dyno). Less