corresponds to the left-most grid line, which is 886.8 mm to the left of
the center. The last column corresponds to the right-most grid line,
which is 886.8 mm to the right of the center.
The figures in row K-Y measure the displacement from the black
separation to the yellow separation for corresponding grid lines. C-Y
measures the displacement from the cyan separation to the yellow
separation. M-Y measures the displacement from the magenta
separation to the yellow separation.
Looking at the K-Y row in detail, the -1.38 in the column where X is
-886.8 indicates the black separation is 1.38 mm to the left of the
yellow separation at the left edge of the sheet. The 1.40 mm in the
column where X is 886.8 indicates the black separation is 1.40 mm to
the right of the yellow separation at the right edge of the sheet. Thus,
the black separation is larger than the yellow (by about 1.38 + 1.40 =
2.72 mm). This is expected because the black was printed before the
yellow, and the paper grew while traveling from the black ink unit to
the yellow ink unit. The growth of the black separation, relative to the
yellow, is (1.38 + 1.40) / (2 x 886.8) = .157%, as shown in the %age
Growth column at the right of the table.
Similarly, for the C-Y and M-Y rows, the growth of these separations
relative to yellow is calculated in the same way and shown at the right
of the table. The growth of the cyan is about twice that of the magenta,
while the growth of the black is about three times that of the magenta.
This is normal for equally spaced ink units.
Note: The only data used to compute the growth was the displacements at the
outer edges.
After you calculate web growth, you enter the percentages into the
web growth profile for the press and paper to which this growth
applies. You must enter values for both the upper and lower surfaces in
the same web growth profile. Prinergy takes the percentages from the
web growth profile and uses an algorithm to compensate for the web
growth. The numbers in the web growth profile should decrease from
the first ink tower (first down, so largest growth) to the last ink tower
(last down, so no growth).
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Note: Only horizontal percentages appear in the file. If a percentage is missing, as
it is for all the y (along-the-web) parameters, it is assumed to be zero. The growth
for tower 4 (corresponding to yellow, according to the
TowerColorMap.txt
file) could therefore be left out, given that it is zero. For true web growth, the
percentage growth values for the lower surface (side=L) are the same as for the
upper surface (side=U) to avoid the paper curling.
Web growth
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