No Metric Aggregations Unavailable

I am using Kibana 6.8.1 with Elastic Search 6.8.1.
I would like to create a serial difference aggregation but it seems that only metric aggregations are available (see figure). All the other aggregations are gray.Screenshot%20from%202019-08-07%2017-54-57

TSVB won't let you select those because you haven't configured numeric metrics as separate series- for example, you may need to configure "Average of bytes" before you can select "Derivative of bytes". Then you can choose whether to display the original number or just the computed value.