🚀 go-pugleaf

..what was omitted is that all these different hardness scales give
different hardness numbers (even if they are all converted to the same
units, e.g GPa or kgf.mm^-2). It is even possible for two materials
which have the same hardness on one scale to be different ahrdnesses on
another - this is because each test actually involves a bundle of more
fundamental properties: yield stress, elasticity, strain-haredning 
ciefficient just for starters.

Most research on indentation uses cones or pyramids because the stress
analysis is more straight forward, i.e. Vickers or Knoop indenters.

For just ordinary quality assourance one of the Rockwell series of tests
is easiest because it measures the difference in indentation depth
between a minor and an major load, so is more robust to errors in setup.
--Philip
ref: "Factors affecting the microhardness of solids", PhD thesis, Univ. of
Cambridge, UK., 1979, P.M.Sargent
--
-Philip Sargent
Cambridge University Engineering Dept., Design Centre & Materials Group