The Cut and Fill Convention
When calculating prism volumes, it is important to remember which way round the volume is being calculated. If your project surfaces A to surface B and then reverse the process by projecting surface B to surface A, you will end up with two sets of results. The volume of cut or material in the first projection will be the same as the volume of fill or void in the second.
The convention that has been adopted by n4ce is that where the current surface is above the second surface, this is considered to be cut or material. Historically, this is how n4ce and its predecessors have always worked, and whilst it is perhaps the wrong way around, we cannot change it now as this would create confusion amongst our users. In a simple example where you have designed a screening bund and projected it to an OGL, the volume will be shown as cut or material when really it should be fill or void.
When checked, the Swap Cut & Fill check button allows you to switch the results so that they are presented in the correct way in either reports or tables. If you are viewing a design surface on screen, with its associated groups, and you are projecting to an OGL, then you must swap cut and fill by ensuring that the check button is ticked. Conversely, if you have the OGL on-screen and are projecting to a design surface, this button should not be ticked.