Dynatrace uses different ratings and scores to measure the performance of your application as well as the user experience it delivers.
These ratings are especially handy when you have a number of applications and want to get a quick overview of their states or compare their performance. There are a number of metrics, such as visually complete or the number of errors produced, to make such comparisons. However, because applications vary in so many ways, it's sometimes not so helpful to make 1-1 comparisons using specific metrics. For example, a median Visually complete measurement of 5 seconds for an image gallery application might be fine for its end users while a 2-second lag for a plain-text news application would be unacceptable.
In such cases, comparing only the raw metrics isn't optimal. Scores and indices give a better picture because they combine different metrics and rules into a single number that factors in the individual thresholds defined for each of your applications. Scores and indices enable you to look at a single number and see if your applications are healthy and your users are satisfied.