Something that's been bugging me for a while, and happy I've finally cracked! there might be a less-expensive way todo it, but seems to work ok for me..
Pretty basic 2D Linear Interpolation, I'm not sure if you would call this piece-meal interpolation or not..

check attachment below for better source too.

double tbl_rpm_to_duty[11][2] =
  {
    {8600, 15},
    {6600, 10},
    {6000, 9.0},
    {5000, 8.0},
    {4500, 20.0},
    {4000, 8.0},
    {3500, 7},
    {3000, 7},
    {2000, 6.9},
    {1000, 6.5},
    {800, 7.5 }
  };


/**    

      
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