The next important differentiation is speed classification. There are three types of speed classes which apply particularly to sustained data rates: Speed Class, UHS (Ultra High Speed) Speed Class and Video Speed Class – which are indicated by symbols on the card denoting the minimum sequential write speed of the card. Speed Class is denoted by a specific class number within a circle. UHS is denoted with the specific class number within a “U,” while Video Speed Class is denoted with a specific class number subset under a “V”. Speed class is of particular importance when detailing the type of data being written in the application since using the wrong speed class card can affect the data being stored. This is especially the case with high-definition video applications, where a higher speed performance card may be necessary to ensure continuous recording.