Delphi Math单元函数mean怎么用啊?

我是新手,网上很多讲Delphi Math单元函数的,都这么说: 函数 Mean(const Data: array of Double): Extended；这里面的参数怎么传啊?我这么写,根本不行:
var
    bv1,bv2:real;
    subs1,subs2: array[1..dim] of real;
begin
      bv1:=mean(subs1);
end;
抱错: [Error] p1u1.pas(63): Incompatible types
如果写成mean(subs1[1],subs1[2],subs1[3]),也是一样报错!
请各位先辈帮忙!