This guidance is intended to aid drug manufacturers (including ancillary testing laboratories) in calibrating U. S. Pharmacopeia (USP) Dissolution Apparatus 1 and 2 to help assure that critical parameters associated with the dissolution apparatus meet certain mechanical calibration (MC) tolerances. This guidance recommends that an enhanced MC procedure (such as the one recommended in this guidance) can be used as an alternative to the current Apparatus Suitability procedure for Dissolution Apparatus 1 and 2 described in USP General Chapter Dissolution. Regardless of whether the enhanced MC procedure or Apparatus Suitability procedure is used, the guidance also recommends that appropriate measures be taken to control the following sources of significant variability in dissolution testing: dissolved gases, vibration, and vessel dimensions.