Barbault's index is formed by adding up the distances between the 5 outer planets, that is 10 sets. Neptune-Pluto, Neptune-Uranus, Uranus-Pluto, Saturn-Uranus, Saturn-Neptune, Saturn-Pluto, Saturn-Jupiter, Jupiter-Uranus, Jupiter-Neptune, and Jupiter-Pluto. The resulting number calculated over many years will create a graph such as the above. I have calculated the index from 2022 to 2122, I always calculated the value around the time of the vernal equinox every year. I haven't really verified all the values but I think this is about right. These dips that you see above usually signify crisis. Covid and the beginning of the Ukraine War saw really low values. In 2024 they were still rather low...