A method of obtaining a numerical model is disclosed. The numerical model correlates estimated capillary tube output diameter values to minimum pressure for gas bubble generation (MPGBG) values. An MPGBG value of each capillary tube in the reference group is measured for a liquid. An output diameter of each of the capillary tubes is measured by a microscope apparatus. A numerical model that correlates estimated capillary tube output diameter values to MPGBG values for the liquid is calculated.
A method of estimating an output diameter of a capillary tube includes the following steps. An MPGBG value of the capillary tube for a liquid is measured, and the measured MPGBG value is input into the numerical model to estimate the capillary tube output diameter value.
Other methods include a method of estimating an output diameter value of a capillary tube in a test group, a method of estimating and storing output diameter values of capillary tubes in a test group, methods of selecting at least one capillary tube from a plurality of capillary tubes in a test group, and a method of cutting a capillary tube to a desired estimated capillary tube output diameter value.