Returns the standard deviation of the sample represented by a series of non-blank values in a field.
field - any related field, repeating field, or set of non-repeating fields; or an expression that returns a field, repeating field, or set of non-repeating fields.
Parameters in braces { } are optional.
Data type returned 
Originated in 
FileMaker Pro 6.0 or earlier
Field can be any of the following:
a repeating field (repeatingField).
a field in matching related records specified by (table::field), whether or not these records appear in a portal.
corresponding repetitions of repeating fields in a record (repeatingField1;repeatingField2;repeatingField3), if the result is returned in a repeating field with at least the same number of repeats.
several fields in the first matching record specified by (table 1::field A, table 2::field B,...). You can name a different table for each field (table 1::field A;table 2::field B...).
A portal displays the related values 5, 6, 7, and 8 in a field called Scores. StDev(table::Scores) returns 1.29099444....
In the following examples:
StDev(Field4) results in an error because standard deviation of a single number is not defined.
StDev(Field1;Field2;Field3) returns 2.64575131..., 3.05505046..., 2.12132034..., 2.82842712... for a repeating field.
Note  When a referenced field is a repeating field, the StDev function returns the standard deviation in the first repetition fields, then the standard deviation in the second repetition fields, and so on.
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas