There are many types of liquid crystal displays, each with unique properties. The most common LCD that is used for everyday items like watches and calculators is called the twisted nematic (TN) display. This device consists of a nematic liquid crystal sandwiched between two plates of glass. A special surface treatment is given to the glass such that the molecules are homeotropic yet the director at the top of the sample is perpendicular to the director at the bottom. This configuration sets up a 90 degree twist into the bulk of the liquid crystal, hence the name of the display. The twist is visible in the following animation.