Below is a list of sources of audit evidence:

(i) The chief accountant, who is a member of CIMA, explaining why inventory levels are higher at the end than at the beginning of the year.

(ii) A storeman in the main store explaining how the store control system operates.

(iii) An invoice from a supplier of electricity.

(iv) A trainee accountant, presently studying for professional accounting examinations, explaining the reason why telephone charges were lower this year than last.

(v) A letter to the auditor from a lawyer confirming that, as far as he is aware, there are no legal matters of material significance.

(vi) A confirmation from a credit customer agreeing that a balance in the books of the entity is correct.

(vii) A calculation of tax charge and liability made by the auditor.

(viii) Inventory count sheets, the count having been observed by the auditor.

(ix) The company’s order book, showing orders received from customers.

This book is required for company planning purposes.

(x) Estimate of useful life of newly acquired plant made by the production director.

Required:

(a) Suggest which sources may be regarded as reliable, explaining why this is so.

(b) Suggest how you might upgrade the evidence, if required.