Right now, clicking on a barracks, and then clicking on the swordman icon will build 1 swordman.
What if there was a number (0-9) below each unit icon? I could change that number to 3 by clicking an up or down arrow, so that every time I click the unit icon, it would add 3 units to the production queue. Later in the game, if I want to change it back to 1, or to 9, I could click the up or down arrow above and below the number.