#(define Ez_numbers_engraver
   (make-engraver
    (acknowledgers
     ((note-head-interface engraver grob source-engraver)
      (let* ((context (ly:translator-context engraver))
	     (tonic-pitch (ly:context-property context 'tonic))
	     (tonic-name (ly:pitch-notename tonic-pitch))
	     (grob-pitch
	      (ly:event-property (event-cause grob) 'pitch))
	     (grob-name (ly:pitch-notename grob-pitch))
	     (delta (modulo (- grob-name tonic-name) 7))
	     (note-names
	      (make-vector 7 (number->string (1+ delta)))))
	(ly:grob-set-property! grob 'note-names note-names))))))

#(set-global-staff-size 26)

\paper { tagline = ##f }

\layout {
  ragged-right = ##t
  \context {
    \Voice
    \consists \Ez_numbers_engraver
  }
}

\relative c' {
  \easyHeadsOn
  c4 d e f
  g4 a b c \break

  \key a \major
  a,4 b cis d
  e4 fis gis a \break

  \key d \dorian
  d,4 e f g
  a4 b c d
}