int main()
{
	int n,i,k,j;
	double u[1000],sum,ava,sum2,ava2,x;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		sum=0;
		sum2=0;
		scanf("%d",&k);
		for(j=0;j<k;j++)
		{
			scanf("%lf",&u[j]);
			sum+=u[j];
		}
		ava=sum/(double)k;
		for(j=0;j<k;j++)
		{
			u[j]=(u[j]-ava)*(u[j]-ava);
			sum2+=u[j];
		}
		ava2=sum2/(double)k;
		x=pow(ava2,0.5);
		printf("%.5lf\n",x);
	}
	return 0;
}