
double myaverage(double *);
double quaresum(double *);
double junfangcha(double *);

int n;
double sz[100];

int main(int argc, char* argv[])
{
	int k,i,j;
	scanf("%d",&k);
	for(i=0 ; i<k ; i++){
		scanf("%d",&n);
		for(j=0 ; j<n ; j++){
			scanf("%lf",&sz[j]);
		}
		printf("%.5f\n",junfangcha(sz));
	}
	return 0;
}

double myaverage( double *sz )
{
	double x=0.0;
	int i;
	for(i=0 ; i<n ; i++)
		x += *(sz+i);
	x /=n;
	return x;
}

double quaresum( double *sz )
{
	double x=0.0,a;
	int i;
	a = myaverage( sz );
	for(i=0 ; i<n ; i++)
		x += ( *(sz+i) - a ) * ( *(sz+i) - a );
	return x;
}

double junfangcha( double *sz )
{
	return sqrt( quaresum( sz ) /n );
}