int main()
{
	int k,n,i,j,l,m,y;
	double *p[100],*pp[100],a,x=0,b=0,c;
	scanf("%d",&k);
	for (i=0;i<k;i++)
	{
		scanf("%d",&n);
		p[i]=(double * )malloc(100*sizeof(double));
		x=0;
		for (j=0;j<n;j++)
		{
			scanf("%lf",p[i]++);
			x=x+*(p[i]-1);
		}
		a=x/n;
		p[i]=p[i]-n;
		b=0;
		for (y=0;y<n;y++)
		{
			b=b+pow((*(p[i]+y)-a),2);
		}
		pp[i]=(double * )malloc(sizeof(double));
		*pp[i]=sqrt(b/n);
	}
	for (i=0;i<k;i++)
	{
		printf("%.5f\n",*pp[i]);
	}
}