int main()
{
	double shuru[100],*shu=shuru,fangjungen(double *shu,int k);
	int n,k,i,j;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&k);
		for(j=0;j<k;j++)
			scanf("%lf",&*(shu+j));
		printf("%.5lf\n",fangjungen(shu,k));
	}
		return 0;
}
double fangjungen(double *shu,int k)
{
	int i;
	double zong=0.0,pingjun,result;
	for(i=0;i<k;i++)
		zong=zong+*(shu+i);
	pingjun=zong/k;
	zong=0.0;
	for(i=0;i<k;i++)
		zong=zong+(*(shu+i)-pingjun)*(*(shu+i)-pingjun);
	result=sqrt((zong/k));
	return result;
}