Multiply Input And Show Result Automatically

I wanna make simple script that multiply any input by .51 and show the result automatic, without pressing any button, I got two scripts first script add value one to value two and show result auto, other script multiply but I have to press button, how to merge them and if there are script do the job better than those tell me. Input Box, when I input any value the result of multiply that value by .51 appear beside it automatic

Script One:
</head><script type="text/javascript" language="javascript">
function autocalc(oText){
if (isNaN(oText.value)) //filter input{
alert('Numbers only!');
oText.value = '';
} var field, val, oForm = oText.form, total = a = 0;
for (a; a < arguments.length; ++a) //loop through text elements {
field = arguments[a];
val = parseFloat(field.value); //get value
if (!isNaN(val)) //number? {
total += val; //accumulate
}} oForm.total.value = total; //out
} .....