Because log posts are vulnerable to rot from water wicking up the end grain, the author makes the top of the footing 2 inches smaller than the post to provide a drip-edge.
All layout on logs springs from a centerline. To find it, a plumb line is drawn through the center of each end of the log.
After making the cut, the carpenter checks for square, remembering to allow for any taper the log may have.
Anchors are rarely centered exactly on the pedestal, so the author carefully transfers the slot layout to ensure that the post will overhang the pedestal evenly.