The Bagley correction is needed to calculate the inlet pressure drop when round hole capillaries are used. Near the inlet area of round hole capillaries, a pressure drop is resulting from convergent flow in the capillary inlet. In the same way a part of the pressure is also used for the outlet. The Bagley correction is supporting the separation of the viscose pressure drop and the inlet/outlet pressure drop. To determine the inlet/outlet pressure drop the pressure drop is being applied with different capillaries of the same diameter but different lengths and extrapolated to zero (Bagley plot).

The Bagley correction is the first correction applied to highly viscous materials (>1 Pa·s), such as plastics and rubbers. By using the GÖTTFERT 2-barrel capillary rheometer, users have the unique opportunity to perform this correction automatically using the software. After the Bagley correction has been performed, the GÖTTFERT software then carries out the Rabinowitsch-Weissenberg correction. This sequence must be followed for physical reasons and is automatically handled in the correct order by the analysis in WinRheo II.