Send value with submit from output element won't work

I am using the output element in my HTML to show oninput calculations.

This works fine.

But when submitting, only the input values are sent - and not the output value.

How do I sent the output value or the oninput value?

My current code:

<FORM name="order" id="order" action="modelle31a.php" METHOD="POST" onInput="total.value=(Aufkleber_blau.valueAsNumber*1)+(Aufkleber_rot.valueAsNumber*1)+2">
Anzahl <b>Aufkleber</b> blau: <input type="number" name="Aufkleber_blau" value="0" min="0" max="10" maxlength="3">&nbsp;-&nbsp;
Anzahl Aufkleber rot: <input type="number" name="Aufkleber_rot" value="0" min="0" max="10" maxlength="3"><p>
<b>Insgesamt zu &uuml;berweisen: <output form="order" name="total">0</output> &euro;</b>
<input type="hidden" name="onInput" value="total.value">

My thinking/hope was that this line will catch and send the total.value:

<input type="hidden" name="onInput" value="total.value">

So, what is my fault?