ASTDEV_S

Description: Returns the standard deviation of the fitted model at the specified stress level(s). The standard deviation is the square root of the variance.

Syntax: ASTDEV_S(Data_Src, [SL_1])

Data_Src is the source data sheet from which the value is taken.

SL_1 is the stress level, for each stress type, at which the standard deviation is calculated. The number of stress level inputs is determined by the number of stress types in the specified data sheet.

Remarks:

The Data_Src can be one of the following values:

If using a default data source, it must be either 1, 2, 3 or 4, as selected from the Data Source Index drop-down list.
It can take a data sheet name (e.g., "Folio1!Data 1").
It can take a variable name defined in the Defined Names window (e.g., datasource).

SL_1 is an optional value. The default value is the use stress specified in the Use Stress Level window, but you can change the value to any desired number. If the data sheet uses the Cumulative Damage model, you can also use a stress profile for this value.
The variance of the life provides a measure of the spread of the failure times and is given by:

The larger the variance, the wider the spread of the failure times.

The standard deviation is the square root of the variance:

Example:

ASTDEV_S("Folio1!Data 1",300) = 6.1077

Note that this value will vary depending on the source data set.