68 km/sec.

“Font-Ribera and his team…pioneered a method of measuring BAOs by using quasars, which are galaxies that are far brighter than normal due to the activity of a supermassive black hole at their center. As matter falls into the black hole, it grows extremely hot, radiating light at far brighter wavelengths and over farther distances than conventional galaxies. This allowed the scientists to measure the mass distribution of the universe out to 12 billion years.”

By incorporating quasars into the field of study, physicists determine the expansion rate of the universe to within 2.2 accuracy. That rate: 68 kilometers per second (which, for the Douglas Adams aficionados out there, translates into 42 miles per second.) “The uncertainty is plus or minus only a kilometer and a half per second.”