Dynon Avionics EFIS-D10A Pilots Users Guide - Manual (Page 60)

HSI Operation
EFIS-D10A Pilot’s User Guide 6-11
external course command to control the instrument, this course adjustment also works. If the GPS or NAV
device is in a mode where it is ignoring course commands, turning the course knob results in no change on the
screen. This is true when you are in most GPS modes.
SCALE (GPS mode) - This is used to cycle through the three GPS scale modes.
The scale button only exists if the source you are connected to is not providing scale information.