Each blade was set at a fixed width meaning each log was cut identically, regardless of flaws.
In the 1870s, the limitation of log size due to the radius of the circular saw was improved with the introduction of the double circular saw- with one blade atop the other.
[1] Today, head saws are mostly used for cutting logs 16 to 72 inches (0.41 to 1.83 m) in diameter depending upon the type of band mill the saws are mounted on.
More optimized machines now cut the smaller diameters since they are far more efficient and can provide greater production.
Generally, log carriage speeds are adjustable for optimal performance.