DESC: Nitrogen-purged for reliable waterproof and fogproof performance. The 13-7500 and 13-7501 models are hermetically sealed. And, just in case theyre accidentally dropped in the water, they float! BAK-4 prisms, Multi-coated optics and large UV coated objective lenses for bright images from dusk-to-dawn. Easy-grip rubber armoring protects and provides a secure hold-even when wet. The internal compass on the 13-7500 model illuminates without obstructing the field of view allowing you to establish headings as you continue to scan the horizon for markers and hazards.