Many people consider proofreading a document an easy task, particularly if they are very familiar with the document type or topic. Often businesses will ask for an employee, or number of employees to review a document, assuming that many eyes cast over a document will render it error-free. However, untrained proofreaders will almost always produce a document that has one or more obvious errors. This is because the mind has the ability to automatically correct errors during a read of a document (readers think what they see is correct, even if there is an error). Professional proofreaders have undergone extensive training to enable them to learn this specific skill, training their eye to detect errors such as missing letters, missing words, duplicate words, improper word or language useage, incorrect spacing and incorrect English spelling (i.e. Australian, British, American English).