In Hatchet by Gary Paulsen, Brian measures time in two ways. Brian keeps a mental journal, so it is clear that during his time in the wilderness he does not have access to such basic things such as paper and pencil. All Brian has with him as he begins life in the wild, besides the clothes he wears, are some coins, a billfold, fingernail clippers and his hatchet. Therefore, if he is to keep track of time, he must do it in a different manner.
First of all, as the days seem to roll one into the other, he marks time on the stone near the door of his shelter. However, more importantly, he keeps track of time through his real life events. That is, he names these events as they become milestones in his survival. For example, First Meat day becomes important when he kills and provides for himself as he learns to interact with his environment. This event is followed by First Arrow day. By marking time in this way, Brian is really keeping track of the stages of his maturation, growing into a self-sufficient young man.