About the double scales of I.V. Flow Regulators

Many I.V. Flow Regulators are designed with a double scale, that is a graphical layout with two rows of numbers (or other graphic elements) that are used alternatively to set the desired flow rate for the administration.
Despite its clear purpose, it is not obvious to know the actual meaning of each of the two scales and how they should be used.

Similarly to the example above, most of these scales have a 10%/40% mark, meaning that they are suited for liquids of different viscosity. But how should these percentages be understood?
What is not often communicated is that the reference here is the glucose solution: the 10% scale is suited for fluids with viscosity between the viscosity of saline and the viscosity of a 10% glucose solution; the 40% scale is suited for fluids whose viscosity is higher than the viscosity of a 10% glucose solution, up to the viscosity of a 40% glucose solution.
To be more precise, in Phoenix the 10% scale is calibrated using saline, and the 40% scale using a 20% glucose solution, which is a conventional approach.

Since there are no fixed rules on how a double scale should be made, there is complete freedom to create one for purposes other than handling fluids of different viscosity.

Phoenix, for instance, has developed two new double scales:

One scale is dedicated to the two kinds of fluid containers, bag or bottle, which are associated to different fluid head heights;

 These two scales are already part of Phoenix catalogue so you can ask for more information or samples. Nonetheless, in case of specific applications that require a double scale, Phoenix is ready to assist you with the development of a dedicated layout.