Log rotation studies were performed at 14 Finnish sawmills during the years 2003–2005. In the investigation of automatic log rotation, the materialized degree of log rotation for each log was calculated from photos captured from a digital video recording. Rotation errors (D) for individual logs and again the accuracy of the automatic log rotator was determined from optimized angle values of the log measuring system and materialized angle values calculated from the still photos. The accuracy of the log rotation varied considerably between sawmills. The rotation error average of the automatic log rotation varied from –23.6° to +11.4°. This means that in some cases the logs were under-rotated and in some they were over-rotated, on an average. Standard deviation of the rotation error (s) of the automatic rotator varied from 4.4° to 22.9°. The results of the simulation indicated that the performance of the log rotation system can be improved by adjusting the log rotator control. In addition to the zero degree error on an average rotation (or near to zero), the corrected values have a significantly smaller standard deviation of the rotation error, and the number of correct rotations was significantly higher compared to the situation before the adjusted rotation commands. At Sawmill 1, standard deviation of the rotation error was reduced by 40.9% from 14.9 degrees to 8.8 degrees. At the same time the number of correct rotations (–10°≤ D ≤ +10°) increased 4.0 fold from 20.1% to 79.4%. At Sawmill 2, standard deviation of the rotation error was reduced by 23.8% from 10.5 degrees to 8.0 degrees. At this sawmill, the rate of accepted rotations increased 1.9 fold from 42.6% to 81.0%. According to previous research, 2.5° decrease in standard deviation of the rotation error (from 10.5 to 8.0°) in square sawing means about 0.5% increase in value yield. For example with 10 million Û annual sales of sawn timber this means 50 000 Û extra profit.