Inside a computer, numerical values of red, green, and blue define all possible colors, but what we use to reproduce that color will affect the result. For example, the color cyan is 100% green, 100% blue, and 0% red. These numeric values never change, so cyan will always be the same, but only numerically. How that cyan looks on the screen is affected by several factors, but the most common is an uncalibrated screen.
All computer monitors incorporate small variations due to the nature of manufacturing. For example, the blue pixels on a specific monitor could be slightly bluer than another one, even from the same brand and model. If you display the color cyan as defined by its RGB values on such a monitor, it will look slightly bluer than it should. At BenQ, we use high-precision equipment in the manufacturing process to minimize these discrepancies; however, it's practically impossible to eliminate them altogether.
Color calibration helps reduce the impact of those discrepancies on color performance. After manufacturing, a monitor can be color calibrated by the manufacturer or the end-user. A specialized optical tool measures the actual colors produced by a monitor and compares them to reference values. Whenever differences exist, the computer performs calculations to adjust the color and sends a corrected signal to the monitor; then, measurements are retaken. This process is repeated until everything falls within accepted tolerances for the monitor to be considered color accurate.