Hi Ian, don’t hesitate to just “transcribe from the tables”.
In my professional career, I had often to do complex dynamic calculations requiring performance curves of expensive compressors, gas turbines, and even very large electric motors, and often the driver and compressor, both acting together. All that was available was tatty old nth generation copy of a copy of the curves originally drawn on a drawing board, many years before. I was able to pick off values to a table and achieve quite acceptable results in some quite critical applications.
With your polar curves, two decimal places might look elegant, but is probably not justified by the data as an actual definition of potential performance. Treat it as a good estimate, not a quality assured laboratory test result. The main requirement is to have a consistent target, which you may or may not be able to achieve. Consistent means not only the same target each time you have the same relative wind direction, but also a consistent change in target with a change in direction. You will achieve this if you check your table by plotting little sections or even the whole table on graph paper, or if you prefer it, in Excel, and make any small adjustments necessary to achieve a smooth curve through any three or four points.
Then keep a note of what you actually achieve against your target, or even by how much you exceed it. Using any polar diagram will help you more than none, and no speed instrument that I know of will give two decimal places anyway. In the end, I don’t think there are instruments generally available which will tell the difference in speed between two racing yachts when one slowly creeps past the other, only a line judge with a good line of sight can do that. Your polar table will give you a suitable target and you can update it later if better data turns up.
And please come back and tell us how you go, and how you find it, having that data on your display.