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Quantum Scale System
Appendix A - 6
How the Percentage Tare
Value is Calculated
Percentage Tare value is the value expressed as a percentage
(e.g. 5.6%, 2.3%, etc.), that represents the proportion of tare
material in comparison with the gross weight of a
commodity. For example, if the percentage tare value for a
specific individually wrapped confection is 14%, it means
that for a gross weight of 100 grams, the total weight of
individual wrappers is 14 grams.
The percentage tare value (Proportional Tare) is the figure
that should be used to calculate the proper tare to be used
when weighing individually wrapped confections (IWC).
Here is an example illustrating how it is calculated. In order
to determine the net weight of candies, a fixed tare (weight
of the cellophane bag and the twist tie) must first be
deducted from the total gross weight.
Then, the weight of the individual wrappers must also be
deducted. This weight is proportional to the number of
candies in the bag. To determine this weight, two methods
can be used: 1) candies are unwrapped and the individual
wrappers are weighed, or 2) it is calculated using the
percentage tare value (%T) and the gross weight.
The first method, which is a destructive method, should be
used by the IWC manufacturers or importers to calculate the
percentage tare value applicable to their products. This
percentage tare value should then be provided to retailers so
that they can use the second method which is non-
destructive.
Method to be used by the manufacturer or importer for
determining Percentage tare value (%T):
1) Ensure the scale is indicating zero (0).
2) Select a minimum sample of 25 candies.
3) Unwrap the candies, place the unwrapped candies aside
for further weighing, and weigh the wrappers. The total
weight of the wrappers must be at least ten times greater
than the increment size (e.g. at least 20 grams if the scale
has 2 gram increments). If not, unwrap more candies
and add wrappers on the scale until the target weight is
reached.
4) Record the total weight of the wrappers. This is the tare
weight (TW).
5) Leave all the wrappers on the scale platter and add all
the candies that were unwrapped. Weigh all wrappers
and candies together and record this as the gross weight
(GW).
6) Calculate the percentage tare value. %T = TW x 100%
GW
where:
%T = Percentage Tare Value
TW = Tare Weight
GW = Gross Weight