Raymarine Autohelm ST 30 - Manual (Page 31)

ST30 Compass Installation and Operation Handbook 28
4.3 Average Heading
The compass continuously calculates the average course steered. This is
independent of whether the compass is in Lock mode.
To display the average course, simply press and together
momentarily.
LOCK
COMPASS
LOCK
HEADING
AVERAGE
D1797-1
N
The average course is displayed for 8 seconds at which time the display
reverts to the lock display.
Resetting the Average Heading
With the average heading displayed, simply press and hold and
together for 3 full seconds to reset the average (the compass beeps
once to indicate that the average heading is being reset).
Please note...
After 24 hours of continuous operation, the compass will stop calculating
the average heading and the display will flash.