Organs also have buttons called “pistons” which help to change the registration in the middle of a piece. There are “toe pistons” operated by the feet, and “thumb pistons” which are placed just below each manual so that they can be pushed by the thumb while the fingers keep playing. Large organs often have “general pistons” which change any combination of stops across the organ. These are often be computerised so that players can set them up differently depending on the music they are going to play. If several players regularly use the instrument they can each have their own personal settings for the pistons which they can lock so that no one else can change them.