Question Statement:
In a sprinkler catch-can test with $n = 4$ cans, depths caught are $8\text{ mm}, 10\text{ mm}, 12\text{ mm}, 10\text{ mm}$. Mean depth $\bar{x} = 10.0\text{ mm}$. Absolute deviations are $|8-10|=2, |10-10|=0, |12-10|=2, |10-10|=0$, giving $\sum |x_i - \bar{x}| = 4.0$. Then $\frac{\sum |x_i - \bar{x}|}{n \bar{x}} = \frac{4.0}{4 \times 10.0} = 0.10$. Christiansen's $CU$ in percent is: