What does this mean in the AIP

[Trolle]

Reading through the AIP and come across this line for each aerodrome:

Geoid undulation at AD ELEV PSN

I tried to look it up on Google but to no avail. Anybody out there able to interpret it for me?

[hvogt]

Trolle,

according to 2.3 of ICAO Annex 14 the geoid undulation at the aerodrome elevation position has to be measured and reported. The aerodrome elevation position (that is what AD ELEV PSN stands for) is by definition the position of the highest point of the landing area.

Hope this helps.