Eye chart smaller towards the bottom of the chart. The person removes any glasses or contact lenses, and stands or sits a standardized distance from the chart (e.g., 20 feet for the Snellen chart). The person is then asked to identify the optotypes on the chart, starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified any more. The row in which the person can reliably identify symbols defines the visual acuity. One eye is tested at a time. Practically, this is accomplished by covering the other eye with a hand, piece of paper, or a
X̅ and s chart on the other hand, the sample variability is "not" in statistical control, then the entire process is judged to be not in statistical control regardless of what the formula_7 chart indicates. When samples collected from the process are of unequal sizes (arising from a mistake in collecting them, for example), there are two approaches: X̅ and s chart In statistical quality control, the formula_7 and s chart is a type of control chart used to monitor variables data when samples are collected at regular intervals from a business or industrial process. The chart is advantageous in the following situations: The