Unlike management, external auditors only responsibility is to express opinion regarding the truth and fairness of information presented in the financial statements . According to the second field work standard of GAAS, auditor is responsible for understanding and testing the effectiveness of internal control of the client (Textbook, 2012). There are two primary concerns of CPAs about internal control such as control over reliability of financial reporting and control over classes of transactions. Auditors are concerned about fair representation of financial statement with existing internal control (ibid). Moreover, compliance with regulations of the client is another factor for CPA to understand internal control. After KPMG issued incorrect report about its client, New Century enabled to file Form 10-K. Form 10-K is report required by Security-Exchange Commission about internal control (Jacobs, 2009). In the case of New Century, KPMG could not appropriately assess the effectiveness of internal controls operating within the company. Another concern of auditor in assessment of internal control is classes of transaction. Auditors draw attention to classes of transaction, because accuracy of balances highly depend on accuracy of transactions (Textbook, 2012). Therefore, auditor are mostly focused on transaction related objectives. In order to issue opinion on internal control of client‘s financial reporting auditor must go through process of understanding of internal control. Understanding internal control is one of steps for auditor to determine sample size. International Standard on Auditing 530 require auditor to determine appropriate sample size to reduce sampling– detections risk (ISA 530, 2009). Therefore, understanding of clients internal control system will influence other steps on conducting audit. According to Textbook (2012) there are 4 general phases for auditor to reach understanding of internal control