When I add in for the part in red m=1 it prints out "1" in the textbox so the error must be in the part in red.

<script type="text/javascript">
function monthdate(){
var m=number(window.document.myform.mo.value);
window.document.myform.t.value = m;
}
</script>
<form name="myform">
<table><tr><td align="Center"><INPUT TYPE="text" NAME="mo" VALUE="9" SIZE="4"></td><INPUT TYPE="button" NAME="month" VALUE="Calculate month" onClick="monthdate()"/></td><td align="Center" colspan="4"><INPUT TYPE="text" NAME="t" SIZE = ""></td></tr></table>
</form>