Shifts in foil positions relative to their nominal positions, measured 
with respect to the centre of the target module.  These numbers were 
calculated by Robert MacDonald, based on cital measurements from Yuri 
Davydov, and are for the 2002 stack.  (Not sure how this shifts from year 
to year; depends on whether citals were exchanged, I suppose.)

All distances are in microns.  +Z is downstream.  
Shifts are cumulative.  All foils between a lid and a base are shifted
by the same amount.  (So all foils in module UV7 are shifted by 3 microns 
downstream, for example.  And the target PCs are believed to be at their 
nominal positions.)

From the target, moving UPSTREAM:

Target lid:  +1.5
UV lid:      +1.5
Shift in Z:  +3.0 <--- UV7

UV base:     +2.4
UV lid:      +1.8
Shift in Z:  +7.2 <--- UV6

UV base:     +14.9
UV lid:      +3.4
Shift in Z:  +25.5 <--- UV5

UV base:     +3.1
UV lid:      +3.8
Shift in Z:  +32.4 <--- UV4

UV base:     +15
UV lid:      +2.8
Shift in Z:  +50.2 <--- UV3

UV base:     +0.2
UV lid:      +1.8
Shift in Z:  +52.2 <--- UV2

UV base:     +14.1
UV lid:      +1.2
Shift in Z:  +67.5 <--- UV1

UV base:     +1.6
Dense lid:   +2.4
Shift in Z:  +71.5 <--- DENSE STACK

Dense base:  +14.4
PC lid:      +14.1
Shift in Z:  +100.0 <--- PCs


From the target, moving DOWNSTREAM:

Target base: -1.0
UV lid:      -0.7
Shift in Z:  -1.7 <--- UV7

UV base:     -1.3
UV lid:      -15.0
Shift in Z:  -18.0 <--- UV6

UV base:     -15.0
UV lid:      -2.0
Shift in Z:  -35.0 <--- UV5

UV base:     -2.2
UV lid:      -1.3
Shift in Z:  -38.5 <--- UV4

UV base:     -14.6
UV lid:      -2.6
Shift in Z:  -55.7 <--- UV3

UV base:     -3.1
UV lid:      -1.1
Shift in Z:  -59.9 <--- UV2

UV base:     -15.5
UV lid:      -2.4
Shift in Z:  -77.8 <--- UV1

UV base:     +0.8
Dense lid:   -1.6
Shift in Z:  -78.6 <--- DENSE STACK

Dense base:  -13.8
PC lid:      -14.4
Shift in Z:  -106.8 <--- PCs

====================

Total change in stack length: 206.8 microns.