Multiple Certificates can be combined, provided they have been tested for Yield and contain all the tests you want to include on the Combination Certificate. The combined results are obtained using the calculations prescribed by the IWTO.
Combining Yield Results
Wool base, VM, Yield and Clean Weights are all calculated separately using the results from the component lots. Due to this process and the rounding up or down of results, the IWTO formulated results from the Combination Certificate do not always correlate with a manual calculation.
An example of this is the Combined Clean Weight which is simply the sum of the Clean Weights of the component lots. The Combined Yield is calculated separately so the Combined Clean Weight will not always match the Combined Yield on the Combination Certificate e.g.
|Component 1||Component 2||Combined|
|Nett Weight (Kg)||12000||14000||26000|
|Wool Base (%)||60.00||50.00||-|
|Clean Weight (Kg)||8688||8554||17242|
IWTO Combined Yield = Combined Clean Weight x 100 / Combined Nett Weight
IWTO Combined Yield = 17242 x 100 / 26000
IWTO Combined Yield = 66.3%
A manual calculation of 66.3% of 26000kg would give 17,238 kg whereas the actual IWTO formulated Combined Clean Weight is 17,242 kg.
Combining Mean Fibre Diameter, colour or length results
All component lots for any Combination must have a Yield test. This is because when any results are combined, we use clean weight averages of the lots to calculate the combined results e.g. if 2,000 kg of 24.0 micron wool was added to a 24,000 kg lot of 30.0 micron wool, the average would not simply be 27.0 microns as there is a great deal more of the 30.0 micron wool going into the Combined lot. Therefore, if you wish to combine only Mean Fibre Diameter, Colour, Conditioning or Length test results, you must have a complementing Yield test for all component lots to determine the clean weight of each lot. This applies to all wool lots including scoured and carbonised. N.B. Colour results are only valid for 6 months after testing, if you wish to add a colour result which is older than this onto a Combined Certificate, the wording "Colour reading expired" must be included on the Certificate.
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