> load ('jstests/core/timeseries/timeseries_simple.js')
...

> db.timeseries_simple.createIndex({"time":1, "usage_system":1})
{
	"ok" : 0,
	"errmsg" : "BadValue: Invalid index spec for time-series collection: { time: 1.0, usage_system: 1.0 }. Index must be on the 'time' field: usage_system: 1.0 Command request: { createIndexes: \"timeseries_simple\", v: 2, indexes: [ { key: { time: 1.0, usage_system: 1.0 }, name: \"time_1_usage_system_1\" } ], ignoreUnknownIndexOptions: false }",
	"code" : 67,
	"codeName" : "CannotCreateIndex"
}