Acer 99sl User Manual page 17

Note:
)
The degree of each parameter is present by numeric statement and
corresponding scale.
)
The on-screen menu will automatically disappear after 20-second's
inactivity. If changes have been made, the monitor will automatically
save them.
)
To set the timing and the refresh rate, see the user's guide of your video
card.
Resolution
3-7 Adjusting the Monitor
Maximum Vertical
Refresh Rate (Hz)