How to apply metric aggregation on calculated fields?

Hi I’m new to Grafana and Elasticsearch. Currently I’m using Grafana 7.4 and an index that was populated by njmon. Due to issues, I’m unable to use metricbeat for server monitoring. My dashboard is looking to display cpu utilisation % and the p95 percentile as heatmaps.

  1. To get the cpu utilisation %, I’m adding kernel % and user % by using “Add field from calculation” and alias the result as ‘cpu%’.
  2. But there seems to be no option to store this cpu% result and apply percentile to it. Is there a way to store the result in Grafana for further aggregation?