opacity needs better keyboard shortcuts....

It's fine that we can adjust the opacity with the keyboard number: 1 ='s 10% 2 ='s 20%, and so on, but it would be more helpful that we could adjust with the keyboard down to 9% and 5% and every number between one and 10%..... 

Sometimes, depending on the brush size, bristles selected, and bristle spacing at a setting of 4% it is too opaque, and although it may seem convenient to software designer, when you are adjusting the opacity a lot -- reaching up to the slider and then having to select it and use arrow keys to fine tune the opacity, it can be a hassle; whereas, if with a keyboard shortcut, like changing the size of the brush with the bracket key, if we could adjust the opacity with repeatedly pushing the one(1) key to move between zero and 10% and then each key likewise, this would truly be a helpful keyboard shortcut....

Thanks....