That sheds some light. The bladder on mine is in new condition with no sign of holes or deterioration. The measurements in the photos here are a bit misleading visually. In each case the rule starts right on the edge although the metal clip gives a different impression, Sidewise the cover has a bend; the measurement straight across is about 4 and 1/8″; with the rule wrapping against the bend, it’s about 4 and 3/16th. Lengthwise, it’s a bit over 11 and 3/4″. Dealing with this melodica may be beyond my pay grade in any case, but I’m curious about it.