Hach ULTRATURB sc User Manual page 25

Maintenance
The turbidity of this parent solution is 400, stated in Formazine Attenuation Units
(FAU) or Formazine Nephelometric Units (FNU). This solution can be stored in a
dark place at 25 °C (±3 °C) (77 °F (± 5.4 °F)) for around 4 weeks.
Formazine reference solution
Dilute the parent solution with the aid of pipettes and measuring flasks to produce
reference solutions in the required range. These solutions can only be stored for a
very limited period.
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