How to set pierce height of plasma cutting machine?

Rotate the IHS Delay button to set pierce height.But now we don’t know the value,so we need to set a value randomly.And change it after we get the distance between the torch and the plate as below.The final distance should be 5mm.

i. Press  the torch will move down and torch the plate, then the torch moves up to the set height.Now we measure the distance between the torch and the plate.

ii. If the distance is more than 5mm,we need to decrease the value.If less than 5mm,we need to increase the value until we get the correct distance.