Knowing the approximate viscosity, pick four standard tubes closest in viscosity to your sample Fill the sample tube with liquid, insert a cork, and then using the tube holder insert the four lettered tubes and the sample tube into the holder Turn over the holder and visually compare what letter best matches the rise time of the bubble in the sample The rise time in seconds of the sealed tubes and samples can also be determined using a basic timer Please be aware of the following accuracies when performing the test: Temperature control: 1°C = 10% error Verticality control: 5° slant = 10% error Tube I.D. control: 0.1mm = 2% error