Artikel 66

Spaces used exclusively for the navigation of the ship, which have not been exempted under Article 57, shall be deducted from the gross tonnage to the extent of what is considered reasonable.
The deductible navigation spaces will generally include rooms for keeping and using charts and instruments of navigation, wireless telegraphy and telephony spaces,1) But not the waiting-room for passengers.rooms for keeping navigation lamps, flags, rockets, etc., spaces for submarine signalling and sounding apparatus, rooms for automatic-steering compasses, gyrostabilisers or similar apparatus and spaces for the helm, steering-gear, capstan and anchor-gear with chain lockers.
In ships where part of the wheel-house is used as a chart-room, such part shall be deducted.
In cases where the helm, steering-gear, capstan, anchor-gear or similar appliances are situated in rooms larger than is necessary for the purpose, the actual space occupied by each of these appliances shall be deducted; and, in addition, an allowance will be made on every side of the apparatus for the space necessary for its working (in general, not more than 2 feet or 0.610 metre on all sides). The total height to be allowed should, as a rule, not exceed that of an ordinary 'tween-deck space.