Thanks Tom, those are very good links and graphics.
Sort of responding to TDan and Hasse
a good polar diagram, the effect of drift and set, leeway need to be removed, For example trying recording your track while tacking up or downwind going against or with current! There is a huge difference.
Additionally, use of the polars, when you've got meaningful polars, they will provide more effective guidance (Targets) if the software
can also include the effect of current
and a meaningful estimation of leeway.
What I am trying to say, is I think it really does make a difference how you record
your boat's polars and what values you use HDG/STW or COG/SOG and how you account for Drift/Set and leeway.