Easiest way to volume automate a range selection to specific value?

Using the range selection tool to drag a selection’s volume up or down, is there an easier way to adjust to specific level values without having to go back and enter each start/end point into the info line manually? Or can key commands be created so that you can range select and then increase/decrease volume in specific intervals, like .5db for example? Like if I wanted to just adjust by -1db, the only way I know to do this is range select, drag the selection down as close to -1db as I can get it based on zoom level, and then manually click the points and set them 1db lower, which is kind of time consuming. Even having a key command or something that will automate an adjustment in intervals would be really great, but not sure if this can be done.