There’s nothing unusual about a federal judge appointing a technical expert to help unravel convoluted claims during a patent trial. But Judge William Alsup in the Northern District has done something prominent litigators in the Bay Area say they’ve never before seen a judge do.

On Aug. 30, Alsup appointed an expert to testify specifically on damages in Oracle America Inc.’s closely watched suit against Google Inc., which claims the Android mobile operating system violates Java-related patents and copyrights that Oracle acquired when it bought Sun Microsystems Inc. in 2009.