<script type="text/javascript">

function calcul(chiffre1)

{

  result = (parseFloat(chiffre1)+0.35)/0.966;

  document.getElementById('champ2').value = result.toFixed(2);

}

</script><input type="text" id="champ1" value="" Onchange="javascript:calcul(this.value, document.getElementById('champ1').value);">

<br>

<input type="text" id="champ2" value="" disabled="disabled" style="border:0;">