FF is right - it's part of a process not the whole thing ! I do it like this -
1) Show the picture
2) Say that for me the horizon is about x fingers above the cowling
3) Ask the student how it looks for her/him - how many fingers if you like
4) Explain about different heights and importance of sitting at right level for good forward viz
5) Move the picture to show the difference
6) Put it back
7) Ask her/him how it looks for her/himagain - how many fingers if you like
8) Let the student do all that
9) Tell them to remember that picture as they're going to see an awful lot of it
It seems to work - though, centaurus, you could use centimeters instead of fingers just to make sure that the 737 doesn't crash ................