Qiwei ZD-501 portable Turbidimeter measurement principle 90 ° scattered light, measuring range 0-100/0.01NTU 100-500/0.1NTU, minimum indication 0.1/0.01NTU, correction point 6 points, error of indication ± 6% (± 2% F. S), sexual repeability ≤ 0.5%, zero drift ± 0.5% F. S