Correcting autofill function

[mistral]

Need help how to correct one function: there is mistake in of
javascript calculator:
http://www.ebcalc.com/
I used it as offline html.
There is one error: for unknown reason it autofill value in 'Closing
Bid' field - when you fill data into 'Opening Bid' field, same data
automatically copied into 'Closing Bid' field also. This is wrong in
theory and practice, since in ebay auctions 'Opening Bid' does not
equal 'Closing Bid' , this values is not identical. Here is links to
javascript files, but I confused where and what need be edited?

below is js and css files:
http://www.ebcalc.com/js/ebcalc.js
http://www.ebcalc.com/css/ebcalc.css
http://www.ebcalc.com/css/ebcalc_ie_styles.css

Code is complicated enough, and I dont know how this can be adjusted.