Want to work out your performance loss for a tack / gybe or expected boat speed from TWS and TWA in Excel. Then you need to have a look at this.
I’ve created a useful Visual Basic script for Excel that will allow you to do this. There are two user defined functions (UDF) which will perform linear and Bi-linear interpolation within Excel. I’ve included a sample Excel spreadsheet that demonstrates the use. Remember to enable Developer Tools if you want to import or export the VB script itself (Search on how to import and export VB in Excel). You also need to enable macros in Excel for it to work. BiLinearInterpolator_VB.xlsm  is the Excel spreadsheet and BiLinearInterp.zip  contains just the VB script.
The Sheet BiLinear Interpolator has the examples and explains how the functions work.
The boat polar loaded in the example spreadsheet is the detailed 100ft maxi.