int main()
{
	int n,a[100],i,j,s;
	double *b[100],x=0,y=0;
	double ans;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{b[i]=(double*)malloc(sizeof(double)*100);}
	for(i=0;i<n;i++)
	{
		scanf("%d",&a[i]);
      for(j=0;j<a[i];j++)
		{scanf("%lf",(b[i]+j));}
	}
    for(i=0;i<n;i++)
	{
		for(j=0;j<a[i];j++)
		{ x=x+(*(b[i]+j));}
		x=x/a[i];
		for(j=0;j<a[i];j++)
		{y=y+(*(b[i]+j)-x)*(*(b[i]+j)-x);}
		y=y/a[i];
		ans=sqrt(y);
		printf("%.5f\n",ans);                   //???ans?float?????case??0.00001???????wrongans???????
		x=0;y=0;
	}
}

//??????????????????????????????????passed???????????????????????