@Emmanuel Delay Note that min & max are protected symbols and should not be redefined.
Also, FWIW:
(and (>= volume min) (<= volume max)) == (<= min volume max)
Just a hint you can do numbers inside a circle in mtext if I remember correct its a TTF with left 1/2 number right half.
Using xdata is probably the way to go so a line has a hidden diameter.