The Track Count Calculation functions are used to set the Track Count field of the selected files.
The Per album variant ignores disc numbers. The Track Count field will be set to the highest track number in a track's album. This variant only makes sense if you are preserving disc numbers and are ignoring disc numbers when numbering the tracks.
The Per disc variant sets the Track Count field to the highest track number in the track's disc in the track's album. An empty or 0 Disc field is treated as 1. This variant typically makes more sense as it works with single disc and multi disc releases.
The Absolute variant ignores Album and Disc metadata. The Track Count field is set to the number of selected files.
The Maximum variant ignores Album and Disc metadata. The Track Count field is set to the larger of the number of selected files or the highest track number.