In one of the many books published by the Greek astronomer Ptolemy called Optics, Ptolemy reports the results of refraction experiments he conducted by observing light passing from air into water. His results are as follows: angle of incidence = 10.0 degrees, angle of refraction = 8.00 degrees; angle of incidence = 20.0 degrees, angle of refraction = 15.5 degrees. Find the percentage error for each of Ptolemy's measurements.