Tack Assist
The watch uses GPS-based course over ground to determine your course in the tack assist feature, and does not account for other factors that can affect your boat's direction, such as currents and tides. You are responsible for the safe and prudent operation of your vessel.
While cruising or racing into the wind, the tack assist feature can help you determine if your boat is being lifted or headed. When you calibrate tack assist, the watch captures your boat's port 
and starboard 
course over ground (COG) measurements, and uses the COG data to calculate the mean true wind direction 
and the boat's tack angle 
.
The watch uses this data to determine whether your boat is being lifted or headed due to wind shifts.
By default, the tack assist feature is set to automatic. Each time you calibrate the port or starboard COG, the watch recalibrates the opposite side and true wind direction. You can change the tack assist settings to enter a fixed tack angle or true wind direction.