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Audit related services would include the preparation of the tax computation for the client - the auditor is likely to have the specialist knowledge to do that whereas it would be unusual for the client to have anyone within their employment with that specialist knowledge Assurance services are those that a) are not audits or audit related and b) are where the accountant will provide a service at the end of which a positive conclusion is expressed An example would be an exercise covered by 'agreed upon procedures' where the accountant will carry out specified procedures on past data and express a conclusion on their work ... but not an opinion Non-assurance services involve situations where the accountant is asked to provide a service for which no conclusion is appropriate A compilation assignment fits into the category of non-assurance OK?