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