What does Steinbeck mean by "a little town keeps track of itself and all of its units?"
The quote comes from Chapter 4:
It is wonderful the way a small town keeps track of itself and all of its units.
The author goes on to describe the lives of the town's inhabitants like that of a computer, or larger organism (e.g. an ants nest). Every person has particular jobs, particular habits and patterns, and routines.
This is as the result of both human nature - we are cliched creatures of habit. But also necessary of a small (especially regional) town. In order for everyone to survive, but also excel, the town requires a baseline of community, endeavor and 'hive mind'.
This 'hive mind' is what Steinbeck refers to in the next few lines. Despite it being early in the morning, the chores and routines of the townsfolk have ensured that the entire town is aware that Kino's pearl is for sale.
Steinbeck means that people in a small town, such as La Paz, want the town's inhabitants to behave in familiar and established ways. If anyone deviates from their regular ways, people notice and get agitated. Steinbeck writes that if a person "does not endanger the ease and peace of mind or steady unbroken flow of the town," that person can be forgotten (page 40). However, if the person acts differently than what other people expect, the townspeople will immediately notice this behavior. Therefore, when Kino decides to sell the pearl that he found, the entire town of La Paz immediately takes notice, and everyone knows this information seemingly immediately, including the pearl fishermen, the Chinese grocers, nuns, beggars, and the pearl buyers. They wait for Kino, already knowing what price they will offer him for the pearl.