"For instance, if I put the gizmo on my arm it would read 60% skin and 40% hair, but that of course doesn't mean that the rest of my arm past the surface is the same thing."

I'm willing to put my rep. on the line that there is no hair on the inside of these core samples. :)

"but if I am correct then it is perhaps a little bit irresponsible even on an internet board to advertise rumors of 5% nickel based on the handheld thing."

Actually, no one has stated that the rumours are based on the gizmos.... only that it is possible that the gizmos have likely been used to indicate a significant occurrence. In addition, if a core showed 5% over 200 ft., what are the odds that the rest of the core is not the same composition even if the gizmo was not as able to read accurately beyond the surface. For that matter, when a core has been lab tested for a given percentage, why do we assume that the rock between 50 ft. or 100 ft. spacings can be reasonably relied upon to contain similar percentages when calculating a 43-101. If we can trust an extrapolation over feet we can certainly be pretty confident extrapolating over a few inches given the length.