In　this　paper,　comprehensive　geometric　errors,　including　linkage　errors　and　volumetric　errors,　of　a　rotary　table　are　measured　totally　by　employing　a　double　ballbar　and　obtained　by　a　two-step　identification　procedure.　The　derivations　of　the　center　of　the　ball　installed　on　the　table　are　measured　in　the　error　sensitive　directions　with　newly　developed　serial　of　two　axes　controlled　circular　paths.　Hence,　there　are　nine　results　measured　from　three　mounting　positions　of　the　ball　at　the　same　rotation　angle.　These　results　are　used　to　form　the　identification　model　based　on　the　homogeneous　transformation.　Moreover,　a　sensitivity　analysis　method　is　applied　to　select　the　optimum　installation　parameters　of　the　ballbar　to　diminish　the　influence　of　the　inaccuracy　of　the　measurement　parameters.　As　the　mounting　position　errors　of　the　socket　on　the　table　are　inevitable　during　the　installation　of　the　balls,　a　new　correction　procedure　is　developed　as　well.　Finally,　an　experiment　is　conducted　on　the　four-axis　machining　center.　The　comparison　results　between　the　predicted　errors　and　the　measured　results　are　shown　to　verify　the　proposed　method.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.