std
The standard error for the pair of data names given by the strings. If the data names don't exist or the difference "$s1 - $s2" or "$s2 - $s1" does not exist then an exception will occur. The standard error of the differences are symmetric. That is standard error of "$s1 - $s2" is equal to the standard error of "$s2 - $s1".
Return
standard error for the pair of data names given by the strings "$s1 - $s2" or "$s2 - $s1"
Parameters
s1
the name of data set number 1
s2
the name of data set number 2