
int main(int argc, char* argv[])
{
	int n,u,i,j,k;
	scanf("%d",&n);
	int m;
	double q=0,z=0;//he
	double a[1001];
	double b[1001];//jie guo
	for(i=1;i<=n;i++){
		z=0,q=0;
		scanf("%d",&m);
		for(j=1;j<=m;j++){
			scanf("%lf",&a[j]);
			q=q+a[j];}
		
		for(k=1;k<=m;k++){
			z=z+(a[k]-q/m)*(a[k]-q/m);}
        
	    b[i]=sqrt(z/m);
	}
	for(u=1;u<=n;u++){
		printf("%.5lf\n",b[u]);}

	return 0;
}

