order quantity discount calculation

[swguy]

OK. Try replacing process() in ot_quantity_discount.php with this:

    function process() {
       global $db, $order, $currencies;
       $od_amount = $this->calculate_deductions();
       if ($od_amount['total'] > 0) {
         $show_amt = $od_amount['total'];
         reset($order->info['tax_groups']);
         while (list($key, $value) = each($order->info['tax_groups'])) {
           $tax_rate = zen_get_tax_rate_from_desc($key);
           if ($od_amount[$key]) {
             $order->info['tax_groups'][$key] -= $od_amount[$key];
             if (DISPLAY_PRICE_WITH_TAX == 'true') {
                $show_amt += $od_amount[$key];
                $tax_deduct = $od_amount[$key] - ($od_amount[$key] * $tax_rate/100);
                $order->info['total'] -=  $tax_deduct;
             } else {
                $order->info['total'] -=  $od_amount[$key];
             }
           }
         }
         $order->info['total'] = $order->info['total'] - $show_amt;
         $this->title = '<a href="javascript:alert(\'' . $this->explanation . '\');">' . $this->title . '</a>';
         $this->output[] = array('title' => $this->title . ':',
         'text' => '-' . $currencies->format($show_amt, true, $order->info['currency'], $order->info['currency_value']),
         'value' => $od_amount['total']);
       }
    }

[ecomm]

thanks for the reply
seems you are sorta getting closer to the answer
ok still the discount is a little off
eg
sub total 100
disc. -10
tax 10% 8.18
total 89.18

as you can see the total is still out not by much but the more you add the more it is out

the tax seems to be calculating on the correct total amount of the total eg we work out the gst by total
$90/11 =8.18
90-8.18=81.82 exclusive
81.82+10%=90inclusive
thanks again for your time

ps a quick explaination in the code so i know what why this is happening would be great unless it is more than just a couple of lines