Bit 3 reversed the slot ordering in the 13-slot chassis at serial #198487 (around the middle of 1999). Check the slot labelling (silkscreened next to each slot on the main board) to verify the slot order of the chassis.In the new Chassis, the controller card should be furthest from the power supply, then the first digi card, etc.Note: the front cover design has changed on both units to allow for easier filter change, slot order is only reversed for the 13 slot, it remains the same for the 7-slot.