GeoffR's patch lets you increase by 1% increments instead of jumping ahead by 10%. The instructions for Firmware 3.17.3 are here:
https://www.mobileread.com/forums/sho...d.php?t=264271
Look for
patch_name = `Brightness fine control` and change that one to yes, but you might look through the other options, there's some great tweaks included in the patch which just makes reading on the Kobos more enjoyable. I wouldn't be without the patch changes at this point.
Be sure you use the correct patch for whichever firmware version you're running, or update to the newest which is 3.17.3.