It was discovered that the layerON bit mask of the TkID class in
the GISMO code was not consistent with the placement of the fields in
the binary tag for the Tracker and VXD sub-systems. Also, the TkID class
in the RootApps/Event/ space does not place the fields in the same spot
as the GISMO TkID class. 
	First off, don't go and delete all of your simulated events.
They're still good. This is because even when put in the wrong spot, the
fields don't over-write each other. 
	To do reconstruction you will have to make some changes to the
TkID class in RpptApps/Event/V1.0/src/TkID.cxx. Find the method
TkID::layer(). This method and the setLayer method,right below it will
need to be changed. 

Currently, the methods should look like this:

Int_t TkID::layer() const {
  // This returns the layer number from the first 8 bits of m_tag
  Int_t  layer = (TkID::layerOn & m_tag);

  return layer;
}
//____________________________________________________________
void TkID::setLayer(Int_t tag) {
  // setLayer sets the first 8 bits of m_tag to the layer number
  Int_t layerShift = tag;

  Int_t  layer = (TkID::layerOff & m_tag) | layerShift;

  m_tag = layer;
} 
	To be able to do reconstruction dealing with the Tracker and VXD
you will need to change these methods to look like this:

int TkID::layer() const {

    int  layer = (TkID::layerOn & m_tag) >> 21;

    return layer;
};

void TkID::setLayer(int tag) {

    int layerShift = tag << 21;

    int  layer = (TkID::layerOff & m_tag) | layerShift;

    m_tag = layer;
};

	You will also need to change the layerOn mask which is defined
at the bottom of TkID.cxx. You will need to change it from  0x000000FF
to 0x1FE00000. After doing all of this, remake the Event shared library.
All the RootApps packages link to this library so they will need to be
relinked as well.
	
	Confused yet? These changes will allow you to process all of the
events that you have already generated. We are planning on releasing a
new version of the package sometime early next week. The inconsistencies
with the TkID class will be fixed in the simulator and the
reconstruction code but this fix will probably mean that the files you
generated previously will not produce accurate reconstruction's of the
VXD and Tracker if they are used with the new version of the code. So
you may want to copy TkID to another space before you install the new
version of the reconstruction code just so you have a version of TkID
that reads the old, incorrect layout of the TkID tag.
	If I've missed something, or confused you hopelessly, feel free
to ask me questions.

Rob Shanks
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