The surface interval between two consecutive dives.
In case the following dive is a "repetitive dive" (this means, the tissues are not completely desaturated) the surface interval is given in seconds as a real number. If the tissues are completely desaturated at beginning of the following dive, instead of <passedtime> the element <infinity/> must be used.
(see also <surfaceintervalbeforedive>)
<!-- surface intervalof 36 minutes --> <passedtime>2160.0</passedtime>