Ping the submarine by clicking at any grid point. The distance shown is not the straight line distance, but the sum of the horizontal and vertical separation from the submarine (i.e. the change in x plus the change in y). Click and hold to highlight all grid points at the indicated distance.
When the Moving Sub option is selected, the submarine moves in a straight line. Initially the numbers show the distance to the submarine's entry point somewhere on the boundary of the grid, but once this point is located (or any other point on the submarine's path) the blue dots are removed and grid locations will be marked with either a yellow circle showing how long since the submarine was at that particular location, or an X for a location that is not on the submarine's path.
When Q1 only is selected, only positive coordinates are used. Otherwise all four quadrants are included.