A cutting machine for a Venetian blind comprising a head rail, a bottom rail, and a plurality of blind slats. The apparatus comprises an elongated support beam having a distal end with a stationary lower housing thereon, and a distally movable hollow cinch slidably disposed on the lower housing. Several embodiments generate a test signal in response to coupling a device to a device interface, transmit the test signal on the bus, and generate an error signal when the bus signal at the device interface is different from the anticipated bus signal. The trenches are then filled with an easily removed layer.