This article is a good overview to help explain the process of setting up custom metrics.

https://copperegg.com/basics-of-setting-up-a-custom-metric/

Custom Metrics are helpful to to display, alert on and store (up to a year) any performance metric that is POSTed to the CopperEgg API.

Note, the minimum frequency to POST is every 5 seconds and the maximum is 60 minutes.