The Meaning of the Run Number

Input Run Number:

1. External Generator (bggen): encoded in events
2. Internal Generator (particle gun): default value
3. RUNNO FFREAD card: change the run used for CCDB look-up (pull request to remove issued)
4. RUNG FFREAD card: native GEANT (sets non-default internal generator run number?)

Use in HDGeant3/4:

1. Look up calibration constants
   • Note: also affected by CCDB variation
2. Encode in output events

Richard's proposal for HDGeant4:

1. For calibration look-up, hierarchy of sources:
   1. RUNNO
   2. RUNG
   3. run number encoded in input events
2. run number encoded in output events same as that used for calibration look-up

mcsmear has similar issue if user wants to control number used in calibration