Statistic Calu is created for the university students who studying Natural or Human science to do many experiments and get rapidly Average, Standard Error, etc.
This app, thinking of the numbers you enter as Population or Sample and then considering 2 cases, can show you:
Average,
Variance(Sample and Population),
Standard Deviation(Sample and Population),
Standard Error(Sample),
and give you the chance setting the sample/population number(as N). The degree of freedom, for your information, is Number minus 1.