6.2.1 Viscometers shall be mounted in the constant temperature
bath in the same manner as when calibrated and stated on
the certificate of calibration. See Specifications D446, see
Operating Instructions in Annexes A1–A3. For those viscometers
which have Tube L (see Specifications D446) held
vertical, vertical alignment shall be confirmed by using (1) a
holder ensured to hold Tube L vertical, or (2) a bubble level
mounted on a rod designed to fit into Tube L, or (3) a plumb
line suspended from the center of Tube L, or (4) other internal
means of support provided in the constant temperature bath.