  Gravity Probe B, launched 20 April 2004, is a space experiment testing two
fundamental predictions of Einstein's theory of General Relativity (GR), the
geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth
orbit. Data collection started 28 August 2004 and ended 14 August 2005.
Analysis of the data from all four gyroscopes results in a geodetic drift rate
of -6,601.8+/- 18.3 mas/yr and a frame-dragging drift rate of -37.2 +/- 7.2
mas/yr, to be compared with the GR predictions of -6,606.1 mas/yr and -39.2
mas/yr, respectively (`mas' is milliarc-second; 1mas = 4.848 x 10-9 rad).
