External
Once percentage losses of hearing have been established for both ears, they can then be converted to a binaural percentage by using the following formula:
[( 4 x PLH better ear ) + PLH worse ear ] ÷ 5
Apply the following calculation:
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multiply the percentage loss of hearing of the better ear by 4,
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add the percentage loss of hearing of the worse ear, and
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divide the sum of this amount by 5.