SD is the standard deviation, a statistic that describes the discrete distribution of a set of variables.
CV is the coefficient of variation, which is the ratio of the standard deviation to the mean expressed as a percentage.
2S,-2S is the control line, and any control value that exceeds the X±2S limit is determined to be out of control for that batch of results.
For example, if the value labeled on the QC vial for the batch is 20, and the coefficient of variation CV is 5%, then the value you make must be between 20-(20*5%) and 20+(20*5%), and anything outside of that range is an unsuccessful result.
Expanded Information:
Basic Components of a Quality Control Chart
Expected Values - i.e., the center line of the chart;
Target Values - the upper, area between the lower warning limits;
Acceptable range of measured values - the area between the upper and lower control limits in the chart;
Auxiliary lines - one line on each side of the center line and halfway between the upper and lower warning limits.
Mean control chart
Control the concentration and composition of the sample so that it is as similar as possible to the environmental sample, repeat the measurement with the same method for a certain period of time (e.g., analyze a parallel sample once a day), accumulate at least 20 data (20 replicate experiments may not be performed simultaneously
or analyzed two or more times in a day), and calculate the total mean value (μ ) according to the following formula, Standard deviation (s) (this value shall not be greater than the standard deviation value of the corresponding concentration level specified in the standard analytical method), average extreme deviation ( ) and so on.
The order of measurement is the horizontal coordinate, and the corresponding measurement value is the vertical coordinate. At the same time, the control line is made.
Center line - estimated by the total mean ;
Upper and lower control limits - drawn by value;
Upper and lower warning limits - drawn by value ;
Upper and lower auxiliary lines - plotted by value.
When plotting control charts, the number of points falling within the range should be approximately 68% of the total number of points. If less than 50%, the distribution is inappropriate and the chart is unreliable. If seven consecutive points fall on the same instance of the centerline, the data is out of control and this chart is not applicable.
After the control chart is drawn, the relevant contents and conditions for drawing the control chart should be indicated, such as the measurement item, analytical method, solution concentration, temperature, operator and date of drawing, etc.
Baidu Encyclopedia - Quality Control Chart