ABSTRACT
To achieve any degree of precision, the measuring equipment used must be precisely manufactured with reference to the same standard of length. That standard is the metre, which is now defined using lasers. Having produced the measuring equipment to a high degree of accuracy, it must be used correctly. You must be able to assess the correctness of size of the work by adopting a sensitive touch or ‘feel’ between the instrument and work. This ‘feel’ can be developed only from experience of using the instrument, although some instruments do have an aid such as the ratchet stop on some micrometers. Having the correct equipment and having developed a ‘feel’, you must be capable of reading the instrument to determine the workpiece size. It is here that the two main types of length-measuring instrument differ: the micrometer indicates the linear movement of a rotating precision screw thread, while the vernier instruments compare two scales which have a small difference in length between their respective divisions.
