Instrument for indicating the depths and durations of decompression stops required during underwater submersions

In an instrument for determining the depths and durations of decompression stops required to be made by a diver when ascending after a submarine dive, of the type including:

• a first chamber having a resilient wall,
• a second chamber having rigid walls,
• means interconnecting said first and second chambers, said interconnecting means including a restrictor throttle for delaying the transfer of gas from one chamber to the other upon the occurrence of changes in the pressure to which they are both subject;
• the improvement wherein said second chamber is formed as a cylindrical chamber of a transparent material,
• an inner cylinder is housed coaxially within the cylinder comprising said second chamber, said inner cylinder being at least semi-transparent and communicating with said second chamber through an opening at one end of said inner cylinder, the other end of said inner cylinder being closed,
• a piston slidingly and sealingly housed in said inner cylinder, the position of said piston being observable from outside said second chamber and representing the pressure obtaining at any time within said second chamber, and
• a fixed scale on said rigid chamber against which the position of said piston can be compared to determine the depth and duration of decompression stops required.