int main()
{
	int k,n;
	double shuzu[1001];
	double *p;
	int i;
	double sum1=0;
	double sum2=0;
	double average;
	double S;

	scanf("%d",&k);
	
	for(i=0;i<k;i++){
		scanf("%d",&n);
		for(p=shuzu;p<shuzu+n;p++){
			scanf("%lf",p);
			sum1+=*p;
		}
		average=sum1/n;

		for(p=shuzu;p<shuzu+n;p++){
			sum2+=(*p-average)*(*p-average);
		}
		sum2/=n;
		S=sqrt(sum2);

		printf("%.5lf\n",S);
		sum1=0;
		sum2=0;
	}

	return 0;
}
