We all know that not everything in existence on this earth is perceivable with our senses…( radio waves, x-rays, whale song, etc. ) .
Yet it exists.
We need a medium to make these phenomena perceivable to us.
In my case, it was an air traffic control radar station that made the lines I drew in the air with my Robin 300 visible. Like the lines drawn by a pencil when it touches paper, the secondary traces of radar are captured when the transponder is on. The recording ends when the transponder is set to SBY and recommences when it is turned on again.
The printout of these radar blips ( XREPLAY ) makes it all visible.
An individual transponder code is necessary so that only the traces of a single plane are registered ( eg. 0442 in the case of NOISE  or 0454 in the case of ACHIM )
We are still left with one problem….that of perception.
Actually, to be precise, there are two problems.
Due to the size of these drawings, a person is not able to view it fully, just as one is not capable of discerning the melody in an extremely slow piece of music. 
Our vantage point only allows us to see an airplane flying above us.
It is radar plotting that makes it all tangible for humans.

The flight commenced and ended in Egelsbach ( EDFE in the left corner of the XREPLAY )
Recording time was between 1210 UTC and 1255 UTC, July 16,2009
( Transl: Tony Clark )