Hanna Instruments HI 96101 - Manual (Page 7)

7
PRECISION AND ACCURACY
Precision is how closely repeated measurements
agree with each other. Precision is usually
expressed as standard deviation (SD).
Accuracy
is defined as the nearness of a test
result to the true value.
Although good precision suggests good accuracy,
precise results can be inaccurate. The figure
explains these definitions.
In a laboratory using a standard solution of the
parameter and a representative lot of reagent
(for each parameter) the following standard
deviations were obtained:
Parameter Standard Solution Standard Deviation
pH 7.0 pH 0.1 pH units
Free Chlorine 1.00 mg/L 0.03 mg/L
Total Chlorine 1.00 mg/L 0.03 mg/L
Cyanuric Acid 20 mg/L 1 mg/L
Iodine 2.5 mg/L 0.1 mg/L
Bromine 2.00 mg/L 0.08 mg/L
Iron LR 0.80 mg/L 0.01 mg/L