Details about the absolute and relative thresholds, as well as how to better define anomaly detection rules for Dynatrace monitored entities can be found here: https://www.dynatrace.com/support/help/shortlink/problem-detection-sensitivity
Additionally, for simple, customized alerting, you can also head to 'Custom events for alerting' page within Anomaly Detection settings. This allows you to choose an individual metric and configure a threshold for that metric, as well as filter for particular entities and customize the alert message. Here's a great blog post which reviews this functionality in detail: https://www.dynatrace.com/news/blog/leverage-the-power-of-davis-ai-with-custom-time-series-events-fo...
Hope this helps.