I am trying to understand a figure generated by qualimap titled Coverage Profile Along in Genes http://kokonech.github.io/qualimap/kidney_rnaseqqc/qualimapReport.html .

What is plotted in X axis, I assumed Y axis is normalized read count when I looked at the detailed manual it says -The plot shows mean coverage profile of the transcripts, The X axis is not detailed and any one perhaps advice how they are calculating it.

Thanks