Sensitivity is a useful adjustment if you have a nearby light source triggering the helmet, flourescents or other welders working nearby can be a bit of a nuisance, the delay function is the amount of time the lens stays dark after the arc has stopped, useful when welding at high amps to prevent you from seeing a white or red hot pool when you stop, these controls can also sometimes be used with low amp DC tig to counter the flashing that occurs with some helmets, set the sensitivity to high and the delay to long,