The Raspberry Pi Sense HAT board is normally plugged in to the 40-way connector of the Raspberry Pi. In order to interface external components to the Raspberry Pi in addition to the Sense HAT board, we need to connect the Sense HAT to the Raspberry Pi using either a ribbon cable or jumper wires so that other pins of the Raspberry Pi can be accessed. Therefore, we need to know which pins of the Sense HAT board are used by Raspberry Pi, and which pins of Raspberry Pi are free.