Signaling numbers underwater can be quite complex, with different agencies having different hand signals to represent numbers. With technical diving we count numbers out, all on one hand. This leaves the other hand free for more important tasks, such as holding a line or a torch. Using this method, even complex numbers such as 4.5, 1.30 or 0.70 can be signaled easily.

Note: This is a very quick and very rough and ready video guide!