Your orders to buy stocks are executed by BROKR once per week. This means that when you place your order, we provide an estimation of how many shares you'll buy, based on how much money you want to spend. This means that if, at the time your order is executed, the value of the stock has gone up, you may end up with fewer shares than the estimate.
Similarly, if the value of the stock has gone down, you'll end up with more than the estimate.