int main(int argc, char* argv[])
{
	int k,i,j;
	double sz[100][1000],pj[100],b,s[100];
	scanf("%d",&k);
    
	for(i=0;i<k;i++){
		double sum=0.0,d=0.0;
	    int n;
	    scanf("%d",&n);
      	for(j=0;j<n;j++){
		   scanf("%lf",&sz[i][j]);
		   sum+=sz[i][j];
	}
    pj[i]=sum/n;
	for(j=0;j<n;j++){
    b=pow((sz[i][j]-pj[i]),2);
		   d+=b;
	   }
    s[i]=sqrt(d/n);
	
	}
   
    for(i=0;i<k;i++){   
	printf("%.5f\n",s[i]);
	}
	return 0;
}

