Eye chart smaller symbols until the person cannot identify the symbols. The smallest symbols that can be reliably identified is considered the person's visual acuity. The Snellen chart is the most widely used. Alternative types of eye charts include the logMAR chart, Landolt C, E chart, Lea test, Golovin–Sivtsev table, the Rosenbaum chart, and the Jaeger chart. Charts display several rows of optotypes, which are standardized symbols for testing vision. Optotypes are usually letters, numbers, or geometric symbols. Each row of the chart depicts optotypes of a different size. Typically the largest optotypes are in the top row. The optotypes become progressively
Seven-segment display the digit '6' must be displayed with the top bar lit to avoid ambiguity with the letter 'b'. However, this modern scheme wasn't always followed in the past, and various other schemes could be found as well: In addition, seven-segment displays can be used to show various other letters of the Latin, Cyrillic and Greek alphabets including punctuation, but few representations are unambiguous and intuitive at the same time. Short messages giving status information (e.g. "no dISC" on a CD player) are also commonly represented on 7-segment displays. In the case of such messages it is not necessary for every