Amount of substance

Decided: the grex = exactly 1;15 × 10^1X entities (≈ 6.17235 × 10^23 dec).

Why: molar masses then come out ≈ atomic masses in 1/1,000 lib, the same convenience chemists have with g/mol.

Advantage: chemists' rule of thumb (molar mass ≈ atomic mass) carries over unchanged.

  • Chosen so molar masses ≈ atomic masses in 1/1,000 lib (like SI's g/mol): carbon-12 = 11.998, water = 18.01 (dec)
  • Rejected: exactly 10^1X (5.52 × 10^23 dec) - rounder, but molar masses come out ×0.894; SI's Avogadro number - molar masses off by 2.5%