Bigger master keyboards can be placed on the large lower support arms. The depth of the upper support arms can be adjusted to 4 positions, so the lower keyboard remains visible. The desired height of the stacker can be set easily and quickly using the spring-loaded clamping knob. 10 different heights allow each user to be able to find a position that best suits his/her needs. To optimize the position the upper support arms can be adjusted in 5 steps from 0° (horizontal) to a 20° angle. Self-adhesive rubber pads ensure that the instrument is not damaged and stays in place. The stacker is also the basis for an extension to a third level. By removing the back cover, the stacker 18822 can be inserted to take a third keyboard.