This refers to any moving NPCs in the market. Sandgem is the ideal town to do it in, since only one moves. If the NPC turns, it is 1 advancement, and if it walks, it is 1 advancement.
What I did was open the menu. Then close and open the menu while flipping the coin in the middle to confirm you hit your seed. Hopefully the NPC doesn't move while flipping long enough for you to be sure it is the right seed. Once you are sure, just keep closing and opening the menu until the NPC starts to move from 1 square to another (I do this when he is as far as possible north, which I think is 1 from the wall), pausing him in the middle of the two squares. This is 1 advancement, then you do your journal flips. If you mess up and he walks move, you know what to do, like how many less journal flips.