A telecommunications expert who expresses the probability of a mobile phone being in a particular geographic area as a percentage must demonstrate that the percentage figure is based on specialised knowledge grounded in training, study or experience, and not merely unsupported speculation or industry convention. Where such percentage evidence is wrongly admitted but the qualitative equivalent ('highly likely') was unchallenged and the remaining circumstantial evidence is overwhelming, the error will not constitute a substantial miscarriage of justice.
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