<?php
$capacities = array(50000,200000,5000000);
foreach ($capacities as $c) {
echo sprintf("Capacity of %s will be allowed to overdraw by %s.\n", $c, log($c*1000,4));
}
Capacity of 50000 will be allowed to overdraw by 12.787712379549.
Capacity of 200000 will be allowed to overdraw by 13.787712379549.
Capacity of 5000000 will be allowed to overdraw by 16.109640474437.