Initialization at start of run.  Get quantities from database
 which will be needed in event loop, and set other static variables
 to initial values.

 Determine at start-up which cooked data to add to tree.
 This uses a feature of Decode() but ensures that users of
 this class don't think it is a physics event.

 Decodes all the raw data and applies all the calibrations and BPM
 rotations.  Note: This assumes the event structure remains
 constant.  We check this by verifying a constant event length.
 Also note that in order for cooked data to appear in the output,
everywhere we have fData[cook_key] = function of fData[raw_key],
 we MUST have a line devices.SetUsed(cook_key) if we want it.

 Analysis to include data not corrected for pedestal.
  Can be turned on with fgCalib.
  Much of this looks like VaEvent::Decode...
   BUT DON'T BE FOOLED!

 Analysis-independent checks of event quality; updates event's cut array.

Decoding of crate structure.
 A crate is also called a "ROC" in CODA parlance.
 return code:
    0 = no decoding done (error, or wrong event type)
    1 = fine.

 Store a result from analysis of this event.

 Return an item from the event buffer.

 Return true iff event failed one or more cut conditions

 Return true iff event failed low beam cut

 Return true iff event failed low beam C cut

 Return oversampling timeslot for this event.

 Fill in the true helicity value for an event.  We use this to
 associated a delayed helicity with the earlier event it applies to.

 Return readout helicity as RightHeli or LeftHeli.  (WARNING: This
 is the helicity stored in the data stream for this event, which
 in general is *not* the helicity to use in analysis of this
 event!  See GetHelicity().  Note also that this is the helicity
 bit from the source and does not reflect half wave plate state,
 g-2 precession, etc.)

 Return true helicity as RightHeli or LeftHeli.  (WARNING: This is
 the helicity to use in analysis of this event, which in general
 is *not* the helicity stored in the data stream for this event!
 See GetROHelicity().  Note also that this is the helicity bit
 from the source and does not reflect half wave plate state, g-2
 precession, etc.)

 Fill in the readout helicity value for the previous event.

 Fill in the true helicity value for the previous event.

 Return readout helicity of previous event as RightHeli or LeftHeli.

 Return true helicity of previous event as RightHeli or LeftHeli.

 Return pairsynch (aka realtime) for this event as FirstPS or
 SecondPS, tagging this as an event from the first or second
 window, repectively, of a helicity window pair.

 Return quadsynch for this event as FirstQS or
 OtherQS, tagging this as an event from the first or later
 window, repectively, of a helicity window quad.

 Return event analysis results stored in this event.

 Diagnostic dump of raw data for debugging purposes

 Diagnostic dump of device data for debugging purposes.

 Diagnostic dump of selected data on one line for debugging purposes.

To find a value corresponding to a data key

 Data raw data for adc # 0, 1, 2...  and channel # 0,1,2,3

 Data calibrated data for adc # 0, 1, 2...and channel # 0,1,2,3

 Data from scaler # 1,2,3..  and channel # 1,2,3...

 Rotation to get X or Y depending on xy flag

 Utility routine used by copy constructor and assignment.

 Utility routine used by destructor and assignment.

 Data access functions