Where are the metrics elements specified for the uptime widgets on the dashboard?

[#1]

I am aware of https://hadoop.apache.org/docs/r2.7.3/hadoop-project-dist/hadoop-common/Metrics.html#ClusterMetrics to pull what metrics I want to show in my Grafana dashboard. Problem is, I don't see specifications for the "uptime" metrics show in the dashboard widgets. Where are these documented?

[#2]

Here's a way to edit/add widgets to Ambari http://docs.hortonworks.com/HDPDocuments/Ambari-2.4.2.0/bk_ambari-user-guide/content/adding_a_widget...