the ST60, when connected to the ST60 Tridata or ST60 speed log WILL indicate TRUE WIND speed and direction, as well as APPARENT wind and direction.
If you disconnect the seatalk cable it will only indicate apparent wind speed and direction.
Your speed log must also be calibrated correctly to allow the true wind to be calculated accurately.
The ST60 mainly measures apparent wind only and calculates true by compting boat speed..IT DOES NOT NEED a compass connected to it..
Now..if ypu are into or down a current, boat speed over ground changes, and as a consequence, the true wind direction and sopeed will change accordingly...
A current smaller than say 2 or 3 knots is not going to make a big difference.
but it does do all that..needs a speed log and a connecting cable...NO COMPASS needed