Entering order amount with clicks in a game

Question

So there's this control in an RTS game that lets you set an order amount. Due to being in a fast-paced games' UI, we cannot afford "slow" numeric input, so clicks are preferred. We also have very limited width, and a wildly ranging acceptable amounts. So this is what we have at the moment:

^{download bmml source – Wireframes created with Balsamiq Mockups}

• Left-Click. +/- 1
• Right-Click. +/- 10
• Shift + Left-Click. +/- 100

Now we get complaints from a few of our users, that they Shift + Right-Click by mistake, they want to order +100 but instead they order +0.

Perhaps we could try setting +1000 on Shift + Right-Click, but that would make it overcomplicated(?). How can we rework this control to allow to place +1/+10/+100 orders within this crammed space and without numeric keyboard input?

Answer 1

Using two different mouse buttons for similar actions seems overly complicated to me. Shift isn't the only keyboard button suitable as a modifier, have you thought about using the keyboard more?

EDIT: The question specifically bans numeric input. Shift/Ctrl/etc. are non-numeric.

EDIT2: The average keyboard is bigger than the average mouse. Therefore it's easier to hit the wrong button on a mouse then on a keyboard (which tends to happen, as indicated by OP). Instead of using two mouse buttons with keyboard modifiers, use one mouse button with more keyboard modifiers. Shift, Cntrl, get creative. Some people use Alt a lot for modifiers or even the spacebar/capslock. LeftClick + T is as much a valid combination as RightClick + Shift, although less intuitive. It is however, more difficult to accidentally hit the wrong combination (which answers the OP's question).