Direction Feedback: Modulated Vibration BPM was decided because it is the most simplistic solution to directional feedback. Difference in EM waves may be indistinguishable depending on how they are interpreted. Mechanical Motion is fallible due to mechanical failure over time. Vibrations are easy to sense even for the blind, and can be distinguished based on where they are felt on the body, lending to the possibility of distinguishing directions. 

Form Factor: Necklaces have the primary issue of being inconvenient for the use of vibrations. Both anklets and necklaces share the issue of small sizing preventing all of the required technology to fit within a chassis. Pocket compass form-factors are easy to lose, aren't as seamless as we want the product to be, and aren't as consistent with giving the proper vibrational feedback.

Interfacing: Microprocessor and Operating System are not an option because the blind cannot visually interact with a display, therefore physical touch systems such as sliders, with braille directions, allow inputs to be possible for the blind. 

Orientation Sensing: Accelerometer Vector analysis measures the change in position of the user to form a vector, and thus a cardinal direction the user is moving in. However, small nuanced movements interfere with this process, such as the swaying of hands as you move, which will influence your measured direction. Using the magnetic field of the earth to establish a direction basis, as well as accounting for changing in orientation of the device during regular movements, allow Orientation sensing to work properly and gather all necessary data for cardinal directions.