Lateral x-ray: 4 marks vs 2 marks Test perfomed using the plate 57 of one brick with 4 x-ray frontal marks and 4 x-ray lateral marks The distances between maps in micron are shown in the following slides (as depend on plate position). Legend: - MAP:FXR4 : map evaluated using 4 x-rays frontal marks - MAP:LXR4 : map evaluated using 4 x-rays lateral marks - MAP:LXR2 min/max X side: map evaluated using 2 out of 4 x-rays lateral marks located on the plate side where x is minimum/maximum. (**) (*) A map is a transformation between stage coordinates and nominal (or detector or what.ever.you.want) coordinates (**) The same mark positions of the case with 4 marks are used to not introduce effects due to the mark position accuracy. The map is obtained by simply setting the other marks as NOT FOUND.

MAP:FXR4 – MAP:LXR4 Distance between maps (micron) The rough positions of the marks used are shown in black (1° map) and in white (2° map)

MAP:FXR4 – MAP:LXR2 minX side Distance between maps (micron) The rough positions of the marks used are shown in black (1° map) and in white (2° map)

MAP:FXR4 – MAP:LXR2 maxX side Distance between maps (micron) The rough positions of the marks used are shown in black (1° map) and in white (2° map)

Comments The distance between MAP:FXR4 – MAP:LXR4 is below 10 micron over the whole emulsion plate The map evaluated with only 2 lateral marks get worse and the distance can increase up to 50 micron on the opposite side of lateral marks. Let compare the 4-marks frontal x-ray map with a 2-marks frontal x-ray map obtained by simply setting as NOT FOUND the 2 marks with higher x positions … And what happen if we evaluate the distance between this map and the 2 marks lateral x-rays map?

MAP:FXR4 – MAP:FXR2 minX side Distance between maps (micron) The rough positions of the marks used are shown in black (1° map) and in white (2° map)

MAP:FXR2 minX side – MAP:LXR2 minX side Distance between maps (micron) The rough positions of the marks used are shown in black (1° map) and in white (2° map)

Final comments Changing from a 4 marks map to a 2 marks map introduces errors in the position estimation. This is also true if you have 4 marks map but you didn’t find 2 marks. This is not expected if you don’t change the map. For examples if you use only a 2 marks map for the entire brick (i.e. in the scan-back). This is due the different number of free parameters available for the transformation (6 in the case of 3 and more marks, 4 in the case of 2 marks). The scaling of Y coordinates cannot be well estimated by measuting only 2 marks (with quite the same Y). 4-marks lateral marks are necessary if you don’t want to manage these large errors (at the beginning of scanback and at the end of the scanforth or every time you change the map).