Thanks for the kind words John. I'm afraid this is a case of "have CAD system -will play". It's the result of taking the word impossible as a challenge. The accuracy does vary with the size of the given angle and the quality of the first guess. The smaller the given angle the better. My error calculations were based on a medium sized angle (60 degrees) and fair first guess (25 degrees). However, even a 90 deg. angle and a poor guess (45 degrees) yields a first iteration of 30.021 deg. and a second iteration within 10E-7.