[Zope] <dtml-bar total-...> is always empty in <dtml-in>

Hi, I have a little problem query my databasetable and get the total value of a numeric field "garantiewert". <dtml-var total-garantiewert> is alwas empty. For example <dtml-var count-garantiewert> works. I'm using zope 2.6.1. <dtml-in SelectGarantiewerte> <dtml-var garantiewert><br> <dtml-if sequence-end> <dtml-var total-garantiewert><br> </dtml-if> </dtml-in> Can somebody help me? Thanks, Patrick