Composite metrics let you define a new higher-level metric by specifying an arbitrary set of mathematical transformations to perform on a selection of native metrics you’re sending us. You “compose” a new higher-level metric using the native metrics you send us as inputs. Alternatively you can think of it as a way to specify complex queries against your native metrics.
To create a composite metrics simply open the Composite Metric Editor.
Edit the composite metric in the editor window.
You can set a display name by editing the stream attributes.
To learn how to use Composite Metrics check out our Tutorial and Language Specification or post a question on StackOverflow using the #librato tag.