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The exact centering can be achieved only in the use of vessels in which precise sphericity, circularity, concentricity of inner surface, vertical center, and uniform geometry are all guaranteed.
The high precision vessel of Takao ensures the vertical center. |
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Off center shaft is a critical factor in erroneous results. Therefore, USP, EP and JP pharmacopeia strictly specify the shaft position so that its axis is not more than 2 mm at any point from the vertical axis of the vessel. However, how should we identify the vertical axis of the vessel?
When the vessel itself has some irregularity, non-uniformity or distortion of the inside vessel, the vertical axis of vessel remains vague and the essential meaning of centering of shaft will be diminished.
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