multiple submit in one form

I now have a filemaker form including one -edit button. I can change the contents of a specific record.

This is how it looks (simplified)

<FORM name="myform" ACTION="FMPro" METHOD="POST">

<P><INPUT TYPE="hidden" NAME="-DB" VALUE="Webexpert">

<INPUT TYPE="hidden" NAME="-Lay" VALUE="L2">

<INPUT TYPE="hidden" NAME="-Format" VALUE="M1Ebackup1.htm">

<INPUT TYPE="hidden" NAME="-Error" VALUE="record_detail_error.htm">

<INPUT TYPE="hidden" NAME="-recid" VALUE="[fmp-currentrecid]"></P>

<TABLE>

<INPUT TYPE=text NAME=Nkjin VALUE="[FMP-Field: Nkjin]" SIZE=30>

<INPUT TYPE="image" src="calcbutton.gif" NAME="-Edit">

</TABLE>

</form>

Now the user can change NKjin by pressing the calcbutton

Now i want to use the form also for changing a hidden entry in the record.

I have a field : questionnumber. This field must be hidden from the user.

I want to include two additional buttons in the above form (and in the table).

Button 1 : pressing this button should increment the contents of questionnumber

Button 2 : pressing this button should decrement the contents of questionnumber.

Could anyone explain me how to proceed with this.

Thanks a lot?

Jitse