Teledyne Benthos’ patented VacuSealed^® glass floats and instrument housings are manufactured from precision-molded spheres to exact specifications. The edge of each hemisphere is ground flat to extreme tolerances. When used for flotation the hemispheres are matched, mated, and then evacuated to an absolute internal air pressure of less than 0.3 atmospheres. After evacuation, a sealant and protective tape are applied around the equator. Spheres sealed in this method are nearly impossible to open due to the force exerted upon them by the atmospheric pressure. In the case of the 43.2 cm (17 in) diameter float, this force is in excess of 880 kg (2000 lbs).