A precise and accurate method of measuring Kendrew model coordinates

Polar coordinates of a Kendrew model of α-chymotrypsin (α-CHT) have been measured with a surveyor's transit and a cathetometer to a high degree of accuracy and precision. Bond distances calculated independently for more than 200 independent amino-acid residues have standard deviations of 0.10 Å or less, the torsion angle ω has a standard error of 7°, and the τ angle is precise to 3°. The measured coordinates of about 1800 non-hydrogen atoms of one molecule of the α-CHT dimer fit a set of idealized polypeptide coordinates with a r.m.s. deviation of 0.17 Å, while the average deviation is 0.15 Å.