int main()
{
	int k,i,j;
	int n[100];
	double a[100][100],all[100],aver[100],sqa[100],s[100];
	scanf("%d",&k);
	for(i=0;i<k;i++){
		scanf("%d",&n[i]);
		for(j=0;j<n[i];j++){
			scanf("%lf",&a[i][j]);
		}
	}
	for(i=0;i<k;i++){
		all[i]=0;
		for(j=0;j<n[i];j++){
			all[i]=all[i]+a[i][j];
		}
		aver[i]=all[i]/(double)(n[i]);
	}
	for(i=0;i<k;i++){
		sqa[i]=0;
		for(j=0;j<n[i];j++){
			sqa[i]=sqa[i]+(a[i][j]-aver[i])*(a[i][j]-aver[i]);
		}
		s[i]=sqrt(sqa[i]/(double)(n[i]));
		printf("%.5lf\n",s[i]);
	}
	return 0;
}

