Delphi中的math函数，比如mean,stddev函数怎么用？(50分)

Delphi中的math函数，比如mean,stddev函数怎么用？

帮助里有啊
function Mean(const Data: array ofdo
uble): Extended;
Description
Mean calculates the arithmetic average of all the values in the Data array
parameter.

function StdDev(const Data: array ofdo
uble): Extended;
Description
StdDev calculates the sample standard deviation (the square root of the
sample variance) of all values in the Data array parameter.

帮助我看了，不是太明白，
谁能举个例子，比如X[1..4]，计算其Mean及Standaed deviation.
像这样的：
procedure TForm1.button1click;
var
x:array[1..4] ofdo
uble;
m:double;
begin
……
m:=mean(x);
end;

接受答案了.