In The Sign of the Beaver, why did Matt make notches on his father's stick?

Basically, Matt made notches on a stick so that he could keep track of time.

Matt's father had advised Matt to make seven notches on each stick and to begin looking for the rest of his family when he got to the seventh stick. Accordingly, Matt's father would be gone for six to seven weeks so that he could fetch Matt's mother, his sister, and the new baby from Massachusetts.

Originally, Matt was the only one who accompanied his father to the Maine territory. They had taken a ship to a settlement at the mouth of the Penobscot River and then found a guide to take them by boat up the river. Then, after branching off to a tributary of the Penobscot River, both had disembarked to make their way on foot through forest land. After substantial traveling, they were finally able to lay claim to their own plot of land and to build a cabin.