Trial Balance Variance Analysis

As per SA 320 - Materiality is a professional judgement by the auditor taking into consideration the auditor's perception of financial information. It is ascertained during the planning stage. You need to take the materiality as a whole for the financial statement as well as performance materiality for certain transaction. In your case cited, materiality is not considered to be appropriate. You cannot take materiality based on the movement from the previous period. However, the same can be used for analytical purpose

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