The Fly Reb watch features an external bezel with raised numbers positioned counterclockwise and a slide rule positioned inside which can be used by the crown at "10". 
 The external crown (Bezel) being with the numbers positioned in reverse on the traditional rings, allows time control with the COUNTDOWN system. In this way the watch reminds the owner how much time is really left to "Time Zero". During a technical decompression and when breathing a given gas, it is very important to have the remaining breathing time RBT (Remain Breathing Time) under control. 
 The ruler allows you to immediately calculate the toxicity of oxygen at different atmospheric pressures. An additional calculation tool for countless uses.