On Field Value Change Event (Error:Nan)

This code good work for "On Field Value Change Event"

But: I use decimal seperator "." in place "," to occur error: "Nan"

It bottom:

{literal}<script>document.forms.editform.value_FieldName2.onchange=function()

{document.forms.editform.value_FieldName1.value=document.forms.editform.value_Fi

eldName2.value*document.forms.editform.value_FieldName3.value;}</script>{/literal}