The most basic NDT method is visual examination, one of the best tool used in manufacturing process to identify surface defects / imperfections on the spot assisted by devices that magnify, qualify or quantify the conditions being evaluated.
Inaccessible areas of parts can be inspected using remote visual examination method. In this flexible fibroscope or boroscope is used with xenon lamp to view internals of the part and can be video graphed. Measurements of the flaw can also be easily done.
Most NDT inspections start with a visual inspection