void main()
{
	double *a[100],b,sum,e;
	int i,n,k,m;
	scanf("%d",&m);
	k=0;
	while(k<m)
	{
		scanf("%d",&n);
		if(n==0)
			printf("0");
		else
		{
		for(i=0;i<=n-1;i++)
		{
			a[i] = (double*)malloc(sizeof(double));
			scanf ("%lf",a[i]);
		}
		sum=0;
		for(i=0;i<=n-1;i++)
		{
			sum=sum+*a[i];
		}
			
		b=sum/n;
		sum=0;
		for(i=0;i<=n-1;i++)
		{
			sum=sum+pow(*a[i]-b,2.0);
		}
		e=sqrt(sum/n);
		printf("%.5f\n", e);
		k++;
		}
	}

}