In our lab we use electronic gauss meters for precise measuring of the various magnetic fields used in our pickup. When I do road trips I like using a small hand model manufactured by the R. B. Annis Company in Indianapolis, Indiana. The unit I use measures from -50-0-50+. The -50 is the South magnetic polarity, the 0 is neutral or no magnetic field, and the 50+ is the North magnetic polarity. This handy gauss meter helps me determine the magnetic phasing of pickups along with magnetic calibration that we perform at my shop.