The Bomb Power Indicator. Fixed to the pipe which goes through the roof and has the BPI Baffle plate fitted to it. This records the air wave from a Nuclear Blast. A very rare piece of kit to find. It originally was a scale of 0 to 5 – Pounds per square inch before they changed to 0 to 50 Kilopascals. Rather than renew the face they just added an insert which covers overt the original scale. Inside the bellow is made from brass/ The reset button is located underneath. The pipe with the chain is the drainage pipe, just in case you had moisture form in the pipe.