Why are images displayed on LCD monitors sometimes unclear?

Some common display modes have been preset into the memory of the LCDs and require no screen adjustment. (Slight adjustments for clock and phase might be needed.) Other modes require adjustments by using the Auto adjustment button and the ScreenManager "Screen" menu. A different signal timing with the same resolution/frequency also requires adjustments. [Reference] Clock / Phase adjustment Clock adjustment: Adjust "Clock" when vertical bars of distortion or flickering appears on screen. EIZO LCD monitors have Analog Video Input, which can convert an analog video input signal into a digital video signal and display an image. In converting the input signal, the monitors need to produce the same number of clock pulses as the dot clock of the input signal (graphics system). If the clock pulse is incorrectly set, some vertical noise appears. Phase adjustment: Adjust "Phase" when horizontal bars of distortion or flickering appears on screen. This function adjusts the sampling timing of converting analog video input signal into digital video signal.