Example 2: Measuring page shifts
In this example, the page shifts used to compensate for web growth are
specified instead of grid measurements, as might appear in a table in
the job jacket when traditional compensation methods are used. In this
example, the ink order is KCMY, measurements are in inches, the
imposition is four across, and pages are 12.5 inches wide.
Table 2: Page shifts to compensate for web growth
Page
Left Outer
Left Inner
Right Inner
Right Outer
K
0.005
0.002
-0.002
-0.005
C
0.003
0.001
-0.001
-0.003
M
-
-
-
-
Y
-0.004
-0.002
0.002
0.004
The left outer black page is moved right by .005 in. towards the center.
The right outer page is moved left by .005 in. towards the center. The
yellow pages are moved out. The magenta separation is not adjusted.
While Table 1 specified the displacement on press, Table 2 specifies
the compensation to be applied. In Table 2, magenta is used as the
base separation. However, the web growth profile always uses the last
ink down as the base separation.
Table 3 below reexpresses the data of Table 2 in the format of Table 1.
Consider the left outer page: the black is shifted .005 inches to the
right, and the yellow .004 to the left. As a result, relative to the yellow,
the black page is shifted .009 inches to the right. Because Table 2
indicates how much to shift each page to align the centers of the
pages, and the pages are 12.5 inches wide, the page center of the left
outer page is at 1.5 x 12.5 inches = 18.75 inches left of the signature
center. The displacement of the black relative to the yellow at -18.75
inches from the center, then, is -.009 mm.
Table 3: Displacements from the yellow separation at page centers
Distance in inches
Negative numbers indicate distances to the left.
Non-negative numbers indicate distances to the right.
Page Growth
X
-18.75
-6.25
6.25
18.75
N/A
K-Y
-.009
-.004
.004
.009
(.009 + .009) / (2 x 18.75) = .048%
C-Y
-.007
-.003
.003
.007
(.007 + .007) / (2 x 18.75) = .037%
M-Y -.004
-.002
.002
.004
(.004 + .004) / (2 x 18.75) = .021%
To compute the growth, we again use only data for the outer pages.
The displacements are accurate to only one significant figure, so
there's no need to use more than two figures for the growth
percentage.
738
Chapter 12—Outputs
