void jun(int n){
	float *a;
	int i;
	float sum=0;
	double pingfanghe=0,s;
	a=(float*)malloc(n*sizeof(float));
	for(i=0;i<n;i++){
		scanf("%f",&a[i]);
		sum+=a[i];
	}
	sum=sum/n;
	for(i=0;i<n;i++){
		pingfanghe+=pow((a[i]-sum),2);
	}
	pingfanghe=pingfanghe/n;
	s=sqrt(pingfanghe);
	printf( "%.5lf\n",s);
}
int main()
{
	int n,k,i;
	scanf("%d",&k);
	for(i=0;i<k;i++){
		scanf("%d",&n);
		jun(n);
	}
	return 0;	
}
