
int main() {
    int k;
    scanf("%d", &k);
    while (k--) {
        int n;
        scanf("%d", &n);
        double *x = (double *) malloc(n * sizeof(double));
        int i;

        double avg = 0;
        for (i = 0; i < n; i++) {
            scanf("%lf", x + i);
            avg += x[i];
        }
        avg /= n;

        double s = 0;
        for (i = 0; i < n; i++)
            s += (x[i] - avg) * (x[i] - avg);
        s /= n;
        s = sqrt(s);

        printf("%.5f\n", s);
        free(x);
    }
    return 0;
}
