int main()
{
	int n,c,i;
	
	double so=0.0,sum=0.0,s,*p;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&c);
	
     double *cj=(double*)malloc(sizeof(double)*c);

	 for(p=cj;p<cj+c;p++){
		 scanf("%lf",p);
		 so+=*p;
	 }
	 so=so/c;
     for(p=cj;p<cj+c;p++){
        sum+=(*p-so)*(*p-so);
	 }
	 sum=sum/c;
     s=pow(sum,0.5);
	 printf("%.5f\n",s);
	 so=0;
	 sum=0;
	 free(cj);
	}
	return 0;
}
