Taking advantage of a desk in the IYC clean booth, a viewport window Category C (Cat.C serial #5; see Fig 1), which has 0.1% AR for IR and 0.2% AR for green, was set in an adapter. The wedge angle is 0.75 deg (+/-0.05deg) and the thickest side was shown by an arrow, and the head of the arrow pointed obliequed surface (Fig 2). On the assembled viewport, the wedge side was marked on the flange.

The adapter set looks like in Fig 3. Fig 4 shows the glass was aligned so that its thinnest side came in the left, while the thickest right; hope you can see the difference. As shown in the figure, the obliqued surface should face to the air side, not to vacuum side.

The alignment (or direction?) of the glass should be determined considering how the assembled viewport window will be attached to the vacuum chamber. Fig. 5 shows the thickest side (again, shown by the arrow) was aligned just in the mid of two throgh holes for M8 screws that will fix the flange to the chamber; with is alignment, we can set the edge in horizontal.

To fix the cross slot screws fixing the lid and the flange body are easily broken on their head slot BE CAREFUL!!! Don't use torque wrenches... believe your own arm's sense of torque. So far, I did not find any leak from the same points of the other viewport assembly; see here, for example. I like 5Nm but you don't need to screw them up up to this amount...

The viewport will be installed at the PR2 chamber.