HIGH-PRECISION STUDIES OF ANTIPROTONS can be carried out in an ion trap. Harvard physicist Gerald Gabrielse takes antiprotons from a beam at CERN, reduces their energy by a factor of 10 billion (in a series of slowing and cooling steps), and then inserts them into the final trap, where their motions are compared with commonplace protons. Strictly speaking what is measured is q/m, the ratio of the particle's charge to its mass. In this respect q/m proves to be identical for protons and antiprotons to within an uncertainty of 90 parts per trillion, a tenfold improvement over Gabrielse's previous best measurement. (Gabrielse et al., Physical Review Letters, 19 April 1999; for a dossier on other antiproton properties see the article by John Eades in Review of Modern Physics, 1 Jan 1999.)