There was an update on the subject of two previous NASA Tech Briefs articles: “Compact, Highly Stable Ion Clock” (npo-43075), Vol. 32, No. 5 (May 2008), page 63; and “Neon as a Buffer Gas for a Mercury-Ion Clock” (npo-42919), Vol. 32, No. 7 (July 2008), page 62. To recapitulate: A developmental miniature mercury-ion clock has stability comparable to that of a hydrogen-maser clock. The ion-handling components are housed in a sealed vacuum tube, wherein a getter pump maintains the partial vacuum, and the evacuated tube is backfilled with mercury vapor in a neon buffer gas.