Beside the scaling percentage box, you'll see an area where you can specify your max trade size. Think of this like a safety circuit breaker -- it will be applied after your scaling percentage number is used. So, for example, let's say you specify that you want to trade 50% of what the system recommends, but that you want a maximum quantity of 3. If the system recommends buying 10 units, AutoTrade will start calculations by saying "Ah, the customer only wants to trade 50% of that... or, in other words, 5 units." But then it will see that you have a maximum quantity of 3 and thus will only trade 3 units, not 5.