The chart is broken into six sections. The atomic number, Z, is plotted on the ordinate against the neutron number, N, on the abscissa. Mass numbers, A, are ringed. Stable and naturally occurring unstable nuclides are shown, along with a few extinct nuclides of cosmochemical interest. The abundance of stable nuclides is quoted in per cent. (Unstable nuclides with half-lives over 1012 yr are included in this category.) Half-lives of naturally occurring unstable nuclides are quoted in seconds, minutes, hours, days and years (s, m, h, d, yr). Data mainly from Lide, D. R. (Ed.) CRC Handbook of Chemistry and Physics 1994–5 (75th Edn), CRC Press.