"A free tool to adjust the gamma and colour levels of your monitor."
Monica is a good way to get an acceptable colour rendering on your monitor.
It is especially important to get good gamma adjustments, to assure you that the basic brightness of your screen is the same as that viewed outside, and with the standards used (the sRGB gamma standard).
In the Monica screen you should use the colour bars to get good grading. This is done when the image is a grey that is as uniform as possible. This way you can calibrate your monitor and get the most out of its resolution and adjustments.