IF I HAVE A NEO MAGNET WITH A BR OF 12,300 GAUSS, SHOULD I BE ABLE TO MEASURE 12,300 GAUSS ON ITS SU

No. The Br value is measured underclosed circuit conditions. A closed circuit magnet is not of much use. Inpractice, you will measure a field that is less than 12,300 Gauss close to thesurface of the magnet. The actual measurement will depend on whether the magnethas any steel attached to it, how far away from the surface you make themeasurement, and the size of the magnet (assuming that the measurement is beingmade at room temperature). For example, a 1” diameter Grade 35 Neo magnet thatis 1/4“long, will measure approximately 2,500 Gauss 1/16” away from thesurface, and 2,200 Gauss 1/8” away from the surface.