An examination (exam) is a test. Many things may be examined, but the word is most often used for an assessment of a person. It measures a test-taker's knowledge, skill, aptitude, physical fitness or ability or standing in some other topic. It is a set of questions designed to measure those things. Examinations change and evolve. They have been used since ancient times. In its widest sense, to examine is to look at something very carefully, perhaps to find the cause of a problem. Someone who is ill may need to go to a doctor for a medical examination. A mechanic may examine a machine to find why it is not working properly. In education an examination is a test to show the knowledge and ability of a student. A student who takes an examination is a candidate. The person who decides how well the student has performed is the examiner. An examination may be a written test, an on-screen test or a practical test. Examples of a practical test may be: driving a car, speaking a language, playing a musical instrument and doing a scientific experiment. An on-screen test is a test which uses the computer. If the candidate is successful he will have passed the examination. If he is unsuccessful he will have failed. In some cases it is possible for a student who has failed to take the exam again another time. A student who passes an examination may get a certificate or diploma. Some certificates are professional qualifications, allowing the person to do a particular job, e.g. plumber, teacher, doctor, lawyer.