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third of an entire fruit volume, which attributes to the achievement of average sugar contents value. Therefore,
measuring juice using a refractometer, extracted from the same size and area measured by the SUNFOREST
H-100 series instrument, shall provide more accurate comparison of sugar contents value.
■ Correlation coefficient and standard error of the calibration model
The predicting performance of a nondestructive measuring instrument can be evaluated by correlation
coefficient((R
2
) and standard error(SEC) of the calibration model.
The correlation coefficient indicates the level of co-relationship between the sugar contents predicted by
calibration model and actual sugar contents of extracted juice measured by refractometer. Bigger the
correlation coefficient of the calibration model, better the definiteness between high sugar contents and low
sugar contents. Thus we can tell the calibration model with bigger correlation coefficient is better optimized
to object fruit. The standard error is the statistic distribution of error range between sugar contents predicted
by calibration model and actual sugar contents measured from the juice extracted. A standard deviation of 0.5
Brix means that among the total number of measurement, about 68% can predict the sugar contents within
the error range of ±0.5 Brix. Thus, in some cases, a measurement error may have larger value than 0.5 Brix.
To create a calibration model with good correlation coefficient and useful standard error, it is
recommendable to make models collected from various range of sugar contents and considerable number
of fruit samples. The correlation coefficient and standard error should be made to be suitable for desired
purposes of instrument use ; make decision of harvesting time or selection of favorable fruit at post-harvest
And the calibration model should be created in consideration of the varieties of fruit and area/time of
cultivation.
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