When an aircraft that receives a clearance as number one to land completes its approach using QFE, express the vertical position of the aircraft in terms of height above the airport elevation during that portion of its flight for which you may use QFE.

Why do we use QFE?

QFE is air pressure at the current ground level. It's used to cause the altimeter to register height above the ground (for a certain area). When sitting on the ground at an airport, dialing QFE into the altimeter will cause it to display zero feet.

How do I use QFE?

Take the airfield elevation which in this example is 550 feet (for Popham airfield). You then find divide that elevation, by 30. Then, you take the 18 and take it away from the current QNH. That will give you your QFE.