Calculated gain compared with another loudness tool

[mooninite]

Hello. I have been using a different loudness tool to tag my collection for years. It's called loudness-scanner on GitHub.

I chose the loudness-scanner tool because at the time (~2019) no other tool supported multi-channel tracks and I have a few. In discovering this tool, which sees more development, I was considering switching. My test with a single album saw significant differences between the calculated gain. I do not pretend to know the math involved so I do not know who would be "right" or "wrong" on their calculation.

Example Track:

loudness-scanner:
Album gain, Track gain, Album peak, Track peak
-8.91 dB, -8.23 dB, 1.000000, 1.000000

rsgain 3.5.3 (Fedora 42):
Album gain, Track gain, Album peak, Track peak
-11.20 dB, -10.40 dB, 1.000000, 1.000000

Both tools claim to use a -18 LUFS reference volume. Is there anything else that may bring differences between these two tools? Any other comments? Thank you.