Mxsmanic wrote:

How do you know when you are exactly overflying a specific spot on the
ground?

an instructor of mine in the past who was amused that I couldn't find a
spot that was directly under the aircraft, took the control and we went
interted. The spot was then clearly visible (despite all the accumulated
junk long forgotten on the floor/under the seats that was now
accumulating on the canopy). He did however made it clear that this was
not the standard procedure expected of the students; planing ahead of
time and looking for the spot before getting there was the preferred MO.

--Sylvain