exa-

In SI, the decimal multiplier prefix meaning 10¹⁸. Symbol, E. The 15th CGPM (1975) added it to SI (Resolution 10).

One exagram (1 Eg), for example, is 1,000,000,000,000,000,000 grams.

Comptes-rendus des séances de la 15^e Conférence générale des poids et mesures, Centenaire de la Convention du mètre et du Bureau international des poids et mesures, Paris, 27 mai-2 juin 1975.
Sèvres: Bureau international des poids et mesures; Paris: diffusion OFFILIB, 1976

Metrologia, volume 11, pages 180–181 (1975).

K. Lidén.
SI Units in Biomedical Dosimetry.
Biomedical Dosimetry. Proceedings of an International Symposium on Advances in Biomedical Dosimetry Held by the International Atomic Energy Agency in Vienna, 10-14 March 1975.
Vienna: International Atomic Agency Agency, 1975.

Page 455. Illuminates the role the adoption of the becquerel played in forcing adoption of the exa.