Acer F51 User Manual page 17

Timings not on the above table may not be supported. We recommend
you set the factory preset timings to have optimum screen image.
We offer you 20 preset modes which are compatible with Windows 95
and Macintosh.
In some rare cases, the screen will appear little noise. It might be
caused by nonstandard signal frequency from the VGA card. It is not a
defect. You can improve it by automatic adjustment or manually
adjusting Phase and Pixel Frequency in the image menu.
When turning off the monitor, the interference lines may appear on your
screen. This is normal situation.
To extend the product life, we suggest you set the power saving function
on your system.
3-9 Adjusting the Monitor