Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Serious, Matter-of-Fact, Understated, Honest
It's no surprise that, in a book dealing with such difficult and inhumane subject matter, the author treats it with the utmost seriousness. There is really nothing at all to make light of, and Levi doesn't even engage in much dark humor. He reports all of the horrors he witnesses in a straightforward way, with only the occasional ironic comment.
Since his aim is to bear witness to the atrocities of Auschwitz, he's also matter-of-fact and precise about actions and events. Here's how he describes part of the prisoners' intake routine:
When the tattooing operation was finished, they shut us in a vacant hut. The bunks are made, but we are severely forbidden to touch or sit on them: so we wander around aimlessly for half the day in the limited space available, still tormented by the parching thirst of the journey. (2.27)
Another description of a medical examination in the infirmary:
These [dysentery patients] are checked every third day. They are placed in a line along the corridor. At the end there are two tin-plate pots, and a nurse with a register, watch and pencil Two at a time, the patients present themselves and have to show, on the spot and at once, that they have diarrhea; to prove it, they are given exactly one minute. After which they show the result to the nurse, who looks and judges, they wash the pots quickly in a wash-tub nearby and the next two take over. (4.72)
Here, it's almost like Levi is following the rule of "Just the Facts, Sir." He's merely telling us what happened, without any embellishments. This understated tone is striking given the kinds of appalling things he's witnessing and experiencing.
And the understatement often works to the opposite effect—it breaks our hearts. Think about his account of the night before the Jews in the Italian detention camp were to be transported to Auschwitz. Everyone knew they were being sent to almost certain death.
And how about this one?
The kitchens remained open, the corvees for cleaning worked as usual, and even the teachers of the little school gave lessons until the evening, as on other days. But that evening, the children were given no homework. (1.10)
No melodrama, no outpouring of emotion. Just "But that evening the children were given no homework." Nothing else really needs to be said, does it? The events speak for themselves.
Levi's tone is also very honest. He doesn't shy away from telling the truth, even when it makes him appear foolish or weak. He makes no bones about being physically weak or trying to take advantage of other workers by making them do more work than he. He describes his own gullibility when he first arrives in the camp and thinks the Potato Peeling Command is an actual work group (2.26). This makes Primo appear to be a totally reliable narrator. Because of this, the reader is very likely to empathize with his experiences—and hopefully heed his implicit calls to be vigilant so that nothing like this will ever happen again.