The data plot shows the similarities between the two sets of trials.  Both have a similar shape, though the board with hoarse hair trial does not extend through the same range of angles.  The trend lines represent the general variation in reflection coefficient with the angle of the board.  For different surface characteristics, the hoarse hair board gives a lower  Kr as expected, though the slope of both trends is nearly parallel.

Difficulties experienced with the experiment include an inability to measure Kr accurately for slopes less than 30 degrees, other wave interactions like diffraction and shoaling, especially at high frequencies.  A second problem is that the amplitude is limited to the range at which combining waves will not break.  The human errors involved include sensor calibration and placement as well as measurement of the board angle and steadiness of holding the board.  The paddle also has a tendency to drift away from its mean position, causing phase changes in the incident wave.