Measure allows the creation of "reports"; full-page summaries of data. These are very free-form; basically, a report can display whatever it wants without restriction.
Your widget is expected to be a Node.js module which exports one function. That function takes two parameters, options and callback. It should call the callback with an object with title and html keys. The title is displayed as the title of the report, and should be plain text; html is a block of HTML which is placed as-is, without escaping, into the body of the report page. Reports are automatically linked from the "Reports" summary page.
A report may contain restricted information. If so, it is possible to restrict the report to be viewed only by authenticated users. To do this, add a requires_authentication: true entry to the output object. Note that authentication has to be enabled in config.yaml, otherwise the report will not be generated at all (a warning is printed in this situation). It is not possible to restrict a report to specific authenticated users; just authenticated or not.