I played for 9 months before I figured out the you can use the arrow keys for the exact number of troops you want to send on any of the troop selection screens. Instead of dragging the slider with your mouse, click the slider once and then use your computer arrow right or left keys to move the slider one troop for each click. If you want to send a bunch of troops click in the general area of the slider where you think that number is and then you can refine it with the arrow keys.

The arrow keys also work on the market trade screen for selecting the quantity of resources to trade.