NEC NP41 - Manual (Page 65)

. Usng On-Screen Menu
[IMAGE OPTIONS]
Adjustng Clock and Phase [CLOCK/PHASE]
This allows you to manually adjust CLOCK and PHASE.
CLOCK ................... Use this item to fine tune the computer image or to remove any vertical banding that might appear.
This function adjusts the clock frequencies that eliminate the horizontal banding in the image.
This adjustment may be necessary when you connect your computer for the first time.
PHASE ................... Use this item to adjust the clock phase or to reduce video noise, dot interference or cross talk. (This is
evident when part of your image appears to be shimmering.)
Use [PHASE] only after the [CLOCK] is complete.