need help with calculation

I have a form and i need to know how to multiply some values but just can't seem to figure part of it out. Here is code:

header jscript:

function a1(gt_large_gage, gt_large_color, gt_large_price) {
	var a = document.getElementById(gt_large_gage).value;
	var b = document.getElementById(gt_large_color).value;
	var c = a * b;
	var object = document.getElementById(gt_large_price);
	object.value = c; 
}
function a2(gt_large_price, gt_large_quantity, gt_large_total) {
	var x = document.getElementById(gt_large_price).value;
	var y = document.getElementById(gt_large_quantity).value;
	var z = x * y;
	var obj = document.getElementById(gt_large_total);
	obj.value = z; 
}

Code (markup):

html form code:

<select name="gt_large_gage" onChange="javascript:a1('gt_large_gage','gt_large_color','gt_large_price');">
<option>Select Gage</option>
<option value="7.52">24 gage</option>
<option value="7.66">26 gage</option>
</select>
</div></td>
<td class="bottomborder" width="20%">
<div align="center">
<select name="gt_large_color" id="gt_large_color" onChange="javascript:a1('gt_large_gage','gt_large_color','gt_large_price');">
<option>Select Color</option>
<option value="15">Brown</option>
</select>
</div></td>
<td class="bottomborder" width="20%">
<div align="center">
<input name="gt_large_price" type="text" id="gt_large_price" size="15" onChange="javascript:a1('gt_large_gage','gt_large_color','gt_large_price');"/>
</div></td>
<td class="bottomborder" width="20%">
<div align="center">
<input name="gt_large_quantity" type="text" id="gt_large_quantity" size="15" onBlur="javascript:a2('gt_large_price','gt_large_quantity','gt_large_total');"/>
</div></td>
<td class="totals" width="20%">
<div align="center">
<input name="gt_large_total" type="text" id="gt_large_total" size="15" onBlur="javascript:a2('gt_large_price','gt_large_quantity','gt_large_total');" />

HTML:

I need the value of 'gt_large_gage' * 'gt_large_color' = 'gt_large_price'

and then

This part is working correctly: value of 'gt_large_price' * 'gt_large_quantity' = 'gt_large_total'

Any help is great appreciated!

 

It is possible that JS parses your variables as strings, which results in miscalculation.. Use parseInt() to get every value that you need from the form. This means that this code:

var a = document.getElementById(gt_large_gage).value;

Code (markup):

should be:

var a = parseInt(document.getElementById(gt_large_gage).value);

Code (markup):

Add some code that checks if the user has entered a number, cause if you type symbols inside the text fields, the calculation will be wrong again..