Which magnetizing method, when used last, renders a part best for easy measurement of the external magnetic field with a field indicator?

Longitudinal magnetization is the method that enhances the ability to measure the external magnetic field with a field indicator after it is applied last. This approach magnetizes the part along its length, resulting in a magnetic field that is aligned with the part's longest dimension. This alignment produces a magnetic field that is more uniform and stable, which is conducive to accurate measurements taken with field indicators.

With longitudinal magnetization, the direction of the magnetic field lines is parallel to the length of the component, allowing for easier detection of any defects that may be oriented along the same axis. Moreover, because the lines of magnetic flux extend outward from the surface, they can be effectively measured with field indicators, facilitating the detection of any leakage fields caused by discontinuities.

In contrast, other magnetization methods such as transverse or circular magnetization might create more complex magnetic field patterns that complicate interpretation and measurement with field indicators. Additionally, while residual magnetization can indicate the presence of defects, it does not consistently produce a quantifiable or easily measurable field compared to the structured field generated by longitudinal magnetization. This makes longitudinal magnetization the preferable choice for clear and effective magnetic field measurement.