Monitor calibration guide
Visual calibration cannot match a hardware colorimeter, but it can take a badly set-up monitor and get it most of the way to correct — which is the majority of the benefit.
Set the conditions first
Calibration is meaningless if the environment changes afterwards. Work in the lighting you normally work in, avoid direct light falling on the panel, and let the monitor warm up for at least half an hour. Set the display to its standard or sRGB picture mode before touching anything — vivid and dynamic modes apply processing that will fight you at every step.
Brightness
Most monitors ship far too bright. For office work in a normally lit room, a luminance of roughly 120 candelas per square metre is the usual target. By eye: turn brightness down until a white page stops feeling like it is glowing, then bring it back up slightly. If you get eye strain in the evening, you are still too bright.
Black level and contrast
Display a step wedge running from black to white. You should be able to distinguish every step at the dark end without the near-black steps merging, and every step at the bright end without the near-white steps blowing out into a single white block.
If dark steps merge, raise the black level or brightness control. If bright steps merge, lower contrast. Adjust one at a time, checking the other end after each change, because they interact.
Gamma
Gamma controls how mid-tones map between input and output. The standard target is 2.2 for general use. A gamma test pattern places a solid grey patch inside alternating black-and-white stripes; viewed from a distance, the patch whose brightness matches its surrounding stripes indicates your current gamma. Adjust the monitor gamma setting until 2.2 is the match.
View this from at least two metres away, or squint. Up close the effect does not work.
Grey balance
Display a mid-grey field and look for a colour cast. A grey that leans blue means the colour temperature is set too cool, one that leans yellow too warm. Adjust the RGB gain controls in the monitor menu in small steps — lowering the dominant channel is usually safer than raising the others, which costs you brightness headroom.
Uniformity
While you have a grey field up, check whether the centre and the edges match. Most panels are brighter in the centre. Anything you can only see by looking for it is not worth worrying about; a visible gradient across a professional panel is a warranty conversation.
Where by-eye calibration ends
You cannot judge absolute colour accuracy visually. Your eyes adapt within seconds, so a cast you can no longer see may still be there and will show up the moment you print or hand a file to someone else. If colour accuracy affects your work or income, a colorimeter costs less than a day of your time and removes the guesswork entirely. For everyone else, the visual pass above is genuinely enough.