In your .xml you should have something like that :
Code :
<y3axis side="right" color="FF000000" grid="0" autoscale="0" min="0" max="100" titleside="right" ydelta="65" titlemargin="40">
<title text="Humidité (%)" alignement="vcenter|hcenter" angle="0">
<font color="FF000000" facename="Arial" size="12" weight="400" italic="1" />
</title>
<labels labelinterval="1" angle="0" format=".1" side="right" hide="0">
<font color="FF000000" facename="Arial" size="12" weight="400" italic="1" />
</labels>
<ticks majorticks="5" minorticks="4" side="right" hidefirst="0" hidelast="0" hideminorticks="0" hide="0" />
</y3axis>
Change format=".1" in format=".3"