When more choices are needed, other types of scanning have to be used. Choices may be arranged in rows and columns. The user locates the desired symbol, and allows the light to move from column to column until it reaches the right one and then from row to row until the desired symbol is lit. For even more choices, the user may have a number of different charts with different rows and columns. With encoding, the user learns to use specific codes for each message.
Encoding can be a very rapid way of expressing lengthy messages.
If mental abilities are better than motor abilities, encoding can provide a greater range of vocabulary options. For example, a vocabulary display may only have room for 10 choices. However, by combining numbers, many more messages can be expressed. Usually, both users and communication partners must know the code or have a chart of the codes available. However, some communication devices work by pressing a number code that generates computer speech.