The crosshair is 19 pixels height and width. Each pixel can be visible or not and have its own color from the list: red, yellow, green, cyan, blue, magenta, white, black. Pixels are grouped in "ranges" according to their distance from center of crosshair. To change the color of pixel range press either number and "-" or number and "=". The colors will shift from red to black and vise versa.
To change the visibility of pixel range press the corresponding number and "backspace".
By default, the crosshair is drawn in the very center of the app's working area. You can move it by pressing "alt" and arrows; "alt+delete" will reset its position back to the center.