More and more dive computers are "air integrated" and show the tank pressure permanently during the dive. Via <tankpressure> it is indicated at a <waypoint>. In particular with so-called "technical diving" several tanks are used which normaly contain different breathing gases. Then several tank pressures are shown by the dive computer, too. Therefore the attribute given with <tankpressure> indicates that tank the pressure value belongs to. In case there is only one tank, or a linked double-tank with only one pressure value measured, the attribute may be omitted.
See also <waypoint>.
<!-- actual pressure 200 bar (only 1 tank is used)--> <tankpressure>20000000.0</tankpressure>
<!-- Two tanks are used in this dive. Inside <equipment> both --> <!-- tanks must be declared via <tank id="tank_air"> and --> <!-- <tank id="tank_o2"> so that the cross-references are valid. --> <!-- breathing gas air: actual pressure 200 bar --> <tankpressure tankref="tank_air">20000000.0</tankpressure> <!-- breathing gas pure oxygen: actual pressure 180 bar --> <tankpressure tankref="tank_o2">18000000.0</tankpressure>