<Form>
<p align="center">Gulden
<input type="text" name="gulden" onKeyUp="this.form.euro.value=Math.round(this.value / 0.0220371)/100 " size="8">
Euro<input type="text" name="euro" onKeyUp="this.form.gulden.value=Math.round(this.value * 220.3710)/100 " size="8">
</Form>