A pedal diagram is a way to indicate the position of the pedals at a certain time. The pedal diagram gives the harpist the possibility to see at a glance the position of the pedals.
A long vertical line indicates the division between right and left foot. The seven shorter vertical lines indicate one pedal each.
A pedal diagram.
The long horizontal line indicates the natural (middle) position. If the pedal lines are above the horizontal line it indicates that the pedal is set to the flat position. If they are below the line the pedal is in the sharp position. For example:
E-major pedal diagram.
C-minor pedal diagram.
Pedal diagrams should be placed above or below the two staves of the score. (See: notating pedal changes.)