-1 7 setxrange
-4 1 setyrange
80 setxunit
80 setyunit
/H{0 0} def
/M{1.5 0} def
/B{6 0} def
/A{0 -3} def
1.2 setlinewidth

M point
[M A] ligne 
pointilles
[H A] (<->) ligne
[H B] (<->) ligne

setTimes
(A) A [2 2] dtext
(B) B [2 2] urtext
(H) H [2 2] ultext
(18 m) H A milieu [2 2] ltext
(30 m) 3 0.3 [2 2] utext
setTimesItalic
(M(x)) M [2 2] drtext