Looking at the image at the bottom of this document:
http://www.installationinstructions.com/FYI/digitaldash.pdf
I would have to assume that tightening the screw raises the bar for lamp turn-on. Notice the high boost screw is in further than the low boost screw.
http://www.installationinstructions.com/FYI/digitaldash.pdf
I would have to assume that tightening the screw raises the bar for lamp turn-on. Notice the high boost screw is in further than the low boost screw.