The Excel document in the link below contains a Visual Basic macro that allows one to compute IBU values using the mIBU method. This document and the Visual Basic code were written by John Koopmans. They are provided here to help other homebrewers who may want to use the mIBU method in an Excel document.
In order to use this Excel document, you'll need to enable macros. In order to edit this macro using LibreOffice Calc, select Tools -> Macros -> Edit Macros. Then, select "Calculate Total IBUs...", "VBA Project", "Modules", "Module1", and double-click on "PostBoilUtilization" to edit the code. Use F9 in the document menu to re-compute with any code changes.
NOTICE: While we hope you find this document helpful, no warranty or suitability for any purpose is implied.