The calibration test fixtures are used to hold all of the diagnostic system components during calibration. It has a raised test tube holder, supported by four small Teflon posts. This holder is used during the calibration process, to hold the test tubes with the activated capsule, and the pH calibration solutions. The fixture is made of an opaque acrylic material. It is attached to the test fixture base plate is a clear plexi-glass block with 6 holes in it, which hold the test tubes, used for calibrating the ph capsule.