I am not a licensed aircraft engineer but in the PPL training didnt we have to show a basic understanding of the operation of instruments ? I can remember after my skills test while still sat in the aircraft having to explain what pressure's worked each instrument.
ASI operates on dynamic pressure from the pito head and static pressure "depending on aircraft type" the static is a small hole on the side of the plane which is small and can get blocked easily,
It is part of pre flight checks to inspect for blockage's on the static hole as well as the pito head "both equally important"
Austerwobbler
