The first thing is to calibrate the the apparent accurately. It should be centred when the wind is directly ahead and read the same on both tacks (assuming no boat/rigging asymmetry). Then the log needs to read spot on it also needs to read the the same on both tacks.
Circles only calibrates the fluxgate compass
. This is not used when displaying true wind with reference to the bow (the simple Raymarine
systems will not usually display a true wind compass
heading, which is effected by the fluxgate
The most common problem with a lot of cruising boats is that the log is inaccurate. Even if reads OK when motoring it often reads different when healed and /or on on different tacks. Switching to true ground wind (the wind that would be felt if you were stationary) which uses the GPS
deriverd SOG is much better because the speed is always accurately calibrated. Unfortunatly Raymarine instruments won't do this