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