Don`t forget most trees don`t grow straight, It all depends on the sawyer, how he see`s the log and what he determines that he can get from it. Most tree`s that are straight from the trunk to the first crown that part will be your 5/12. 6/12, 8/12 boards. It also depends on the species of the tree, your hardwoods, softwoods and pulp tree`s. Even with automated sawmills, it`s still up to the sawyer how the log gets cut. I`ve worked in both automated sawmills and the local bootleg sawmills. Unless the tree is a huge redwood from Oregon you won`t get that many cut sizes. Plus another factor is you have to square up 2 sides of the log to start the milling process there you will loose some of the tree as slabwood. Now with these new wood mizer bandsaw sawmills the log can be laid on the carriage and the saw head moves instead of the log on the carriage. Then the raw cut boards need to be ripped to achieve their right size.
This is the type of bootleg sawmill I worked in when I was around 16. It was hard work, hot in the summer and cold in the winter. But I sure did learn alot from the sawyer.