Automate Your Home Using Go: (page 58) temperature values fluctuating between negative and positive values

I have created the example temperature polling application on a Raspberry Pico W and it is working, however, the reported temperature switches between positive and negative values like this:

```
❯ curl http://192.168.1.241
{“tempC”:31.351,“tempF”:88.4318}%
❯ curl http://192.168.1.241
{“tempC”:-31.845,“tempF”:-25.321000000000005}%
```

At first I thought maybe this was because of a flaky sensor, but I get the same behaviour when I flash the application to another Raspberry Pico.

Any idea why this would happen?