Because one of the critical terms involves the SIN(LON-ALONVT), the largest errors should have occurred farthest away from the reference longitude. Therefore, with the way that the AWIP grid is set up, the largest errors should be in the corners of the map. This is indeed the case on this map. Look at the upper right corner. The forecasted wind vectors there go across the isobars at a much larger angle than they should.
Now here is the same wind field that has been rotated correctly.
Note that the winds in the upper corner have turned to more northwesterly. Also, it was stated that winds near the center of the grid would have a basically imperceptible error, so we should not see much of a difference between the wind vectors in the center on the two plots. This is indeed the case.