What does the SQL Service Response Time metric in dba_hist_sysmetric_history mean? The metric defin

I'm having trouble figuring out the meaning of the SQL Service Response Time"  metric in the dba_hist_sysmetric_history table.  The metric units are given as "Centiseconds per call".  Two other interesting metrics in the table are "User Calls Per Sec" and "Executions Per Sec"

What sort of "call" is meant in the "Centiseconds per call" of the "SQL Service Response Time" metric, and how does it relate to the other two metrics?

Are the "calls" SQL statement executions as tracked in "Executions Per Sec"?  Are the "calls" the ones tracked in "User Calls Per Sec"?  Or are the "calls" something else?