16:21

Chris noticed that when the degraders that are at the beam right position when they are "out" may not be fully removed from the beamline.  It's difficult to make a good 
measurement, but it looks like several cm (~3 cm?).

The degrader that moves out to the beam left side has its inner-most edge roughly flush with the square opening of the polyethylene wall.

It does not seem that the issue is about the slider's center position.  This we checked yesterday and within the judgement of our eyes and limited viewing angle, several people 
independently confirmed that the center of the degrader slider is near the true center of BRIKEN and AIDA with respect to the beam axis.  It appears to be an issue of the 
slider's total track length.  Also it should be noted that the degraders are installed in a somewhat asymmetric way, so the consideration of one opening side of the degraders 
when fully open and another isn't fully out may not be germane.

16:44

We shifted the center of the degrader slider to be about less 1 cm to the beam right.  So now the degraders a bit more symmetric as far as their inner edges are related to the 
opening in the polyethylene wall.

As for the Pb wall, its opening is ~10.5 cm.  The "window" in the Pb wall is slightly shifted to the beam left side.  The left side is ~5.5 cm from the center, where as the right 
side is <5.5 cm from the center.