[xsl] Summing hours-worked values from previous siblings only to determine accrued hours

["Mark" <mark@xxxxxxxxxxxx>]

I am creating a work-report sheet that needs to know the value of working 
hours accrued to the current date for each date. The xml looks like this

<Month name=bAprilb>
<Date day="1">
  <Session task="LS Authorities">
    <Notes hours-worked="2.00" notes="Documented changes from last week."/>
  </Session>
</Date>
<Date day="2">
  <Session task="LS Authorities">
    <Notes hours-worked="2.00" notes="Worked with Wayne resolving $2 border 
cases (see Campfire notes)."/>
    <Notes hours-worked="1.50" notes="Final boarder case resolution and 
655/150 issue."/>
  </Session>
</Date>
</Month>

I can get a Daily total of hours worked with a named template called from 
the Sessions template, but how can I show the hours accrued for all previous 
days?
For the XLM given, My output for the first Date should be bDaily Total: 2.0 
Accrued: 2.0.b
and for the second Date bDaily Total: 3.5. Accrued: 5.5.b

That is, I need to know the value of all *previous* hours-worked and exclude 
any *following* hours-worked. The XSLT so far look like this:


<xsl:template match="Session">
   <fo:table-row>
     <fo:table-cell>
       <fo:block xsl:use-attribute-sets="subdiv1">
        <xsl:value-of select="@task"/>
       </fo:block>
     </fo:table-cell>
   </fo:table-row>
     <xsl:apply-templates/>
   <xsl:call-template name="day-total"/>
 </xsl:template>

<xsl:template name="day-total">
 <fo:table-row>
   <fo:table-cell>
     <fo:block xsl:use-attribute-sets="subdiv3">
       <fo:wrapper xsl:use-attribute-sets="title">
         <xsl:text>Daily Total: </xsl:text>
       </fo:wrapper>
         <xsl:value-of select="sum(Notes/@hours-worked)"/>
       <fo:wrapper xsl:use-attribute-sets="title">
           <xsl:text>Accrued: </xsl:text>
       </fo:wrapper>
<!-- What goes here to select all previous Notes/@hours-worked???
           <xsl:value-of select="sum(?????????????Notes/@hours-worked)"/>
     </fo:block>
   </fo:table-cell>
 </fo:table-row>
</xsl:template>