stat/runtime_clock is a SAP Parameter attribute which is used to control SAP runtime clock information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
stat/runtime_clock defines which clock is used for the runtime
measurements (ABAP commans get run time or transaction ATRA). There are
two clocks in the system: A clock based on gettimeofday and a
platform-specific clock based on a hardware register. The second clock
has better resolution and is less expensive to call, but does not work
properly in all environments.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.