If your monitor is in reasonable adjustment you should be able to place a plastic ruler against your screen and measure the line. Horizontal size is usually a user adjustment. Some variation may occur if you are using a multi-sync monitor. This type of monitor allows a user to select higher dpi settings. If your monitor is in reasonable adjustment you should be able to place a plastic ruler against your screen and measure the height of the line.
Vertical size is usually a user adjustment.
Between the 4th and 5th inch marks on the left side of the scale are 32 horizontal lines, if you have a reasonable quality display in reasonable adjustment you should see 32 lines. Between the 2d and 3d inch marks on the scale is a small square. It is composed of alternating black and white pixels. Colors The web uses a standard palette of 216 colors. The upper left corner square is white.