ABSTRACT
Results depend on calibration techniques, bolt size, the care taken in using the instrument, bolt condition and heat treatment, temperature measurements, and all the other factors we've discussed but, in general, it's probably safe to say the following. Most present-day transit time instruments are capable of measuring the change in length of fasteners to the nearest 0.0001 in. Special instruments are also available that can detect change to the nearest 0.00001 in. These absolute accuracies get less as fastener length increases, if for no other reason than that the digital circuits and display can handle only a fixed number of significant digits. The stretch of threaded rods up to 24 ft in length, however, has been measured with accuracies that are believed to have approached the nearest 0.001 in.
