int main()
{
	int k,n;double sum;double x[100];double a,b,c;double S;
	int i,j;double sum1;
	scanf("\n%d",&k);
	for(i=0;i<k;i++)
    {
    	sum=0;sum1=0;
    	scanf("\n%d\n",&n);
    	for(j=0;j<n;j++)
    	{
    		scanf("%lf",&x[j]);
    		sum+=x[j];
    	}
    	a=sum/n;
    	for(j=0;j<n;j++)
    	{
    		b=(x[j]-a)*(x[j]-a);
    		sum1+=b;
    	}
    	c=sum1/n;
    	S=sqrt(c);
    	printf("%.5lf\n",S);
    }
    return 0;	
}