<tankpressurebegin> puts the fill pressure of the tank at the beginning of the dive, given in Pascal as a real number, into brackets.
Contrary to <tankvolume>, or <tankpressureend>, which can be given, <tankpressurebegin> must be given inside the <tankdata> section, because without this information no breathing gas consumption calculation can be performed.
<tankdata>
<tankdata>, <tankpressureend>, <tankpressurereserve>, <tankvolume>
(see also <tankdata>)
<!-- tank pressure at beginning of dive 210 bar -->
<tankpressurebegin>21000000.0</tankpressurebegin>