Magnetic fields can cause the image to "tilt" on the Apple Two-Page
Monochrome Monitor.
Occasionally, the monitors exhibit a tilt in the screen image, either
to the right or left. The tilt is only noticeable, if you look at the edges
of the screen and notice the amount of black space around the image.
Sometimes the amount of black space is greater or less than the amount on
the opposite end of the screen. Image quality is not affected. Larger
monitors, like the Apple Two-Page Monochrome Monitor, are more likely to
show the effect than small monitors.
If a monitor exhibits this effect, say a tilt down to the right,
rotating the monitor around on its swivel base by 180 degrees will cause the
image to tilt up to the right. What this means is that by rotating the
monitor about 90 degrees in either direction, causes the effect to disappear
with no tilt present. It also occurs in varying degrees, depending on
location. This does not occur with every monitor.
Technical Reason For The Tilt
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This effect is caused by differences in the magnetic fields in different
places, usually where there is a strong magnetic field being caused by
power generators or wiring. A monitor, when set up in one place, may
exhibit no tilt, but, when placed somewhere else, may show the above
effect. To remove all possible outside influence, Apple tests for true
image distortion within large magnetic coils that are designed to simulate
normal magnetic fields (when such fields are present). Thus, when shipped,
monitors are perfectly aligned, and any distortion is related to the
environment into which the monitor is placed.
Why does this occur on the Two-Page display and not on other monitors or on
televisions? There are two reasons for this. First, to improve image
quality and lessen eye strain, Apple attempts to make its displays as flat
as possible. Thus the picture tube is physically flatter than most every
tube on the market today. This presents less image distortion (like bowing
of straight lines) and makes the screen image look more like a single sheet
of paper. However, the tilt effect tends to be more noticeable on large
flat tubes. Competitive, large-screen monitors also show this effect.
The reason televisions do not exhibit this characteristic is that they
"overscan" the screen, using all of the picture tube, thus no black space
is visible on the edges of the screen. Thus, any tilt to the image is hidden
from view. The tilt is there, it just cannot be seen. Macintosh computer
displays cannot use this technique, because all information on the screen is
critical and cannot flow off the screen (like the menu bar).