Physical science is based on Systems International.
No, it isn't, you have this entirely backwards.
SI is based on physical science, and is an arbitrarily selected single metrology, taken from an infinite number of equally rational and elegant possible metrologies.
These themselves are a subset of a much larger infinity of less rational and less elegant metrologies, all of which nonetheless are perfectly workable, albeit less efficient*.
SI is distinctive because it was designed to minimise and simplify conversion factors, while remaining practical for use across a wide variety of use cases.
Previous metrologies tended to be accreted from large numbers of independently developed systems, each optimised for a very specific set of users performing a very specific task, rendering them more difficult to adapt to novel tasks or situations, and more difficult to relate to one another - but often somewhat better
for their original purpose than SI or other related metrologies.
The development of SI marks the culmination of a shift from metrologies that fo one thing very well, to metrologies that do almost everything passably well (but often do nothing as well as its users would prefer). It's a similar shift from quality to quantity as the one we saw in manufacturing, which in the C19th moved from individually crafted mechanisms, to mass produced mechanisms with interchangeable and standardised parts.
That shift leads inevitably to a push for monoculture; A rational and elegant universal metrological system has huge benefits, but those benefits are largely lost unless everyone agrees to use the
same system - hence the word "Internationale".
To take one example - distance - we find that SI uses the metre, which was originally defined based on the dimensions of the Earth, with one metre defined as 1/10,000 of the great circle distance from pole to equator. This is not the first widely adopted distance unit to be based on planetary dimensions - the nautical mile was defined to be the distance implied by a one minute of arc change in lattitude, or 1/5,400 of the great circle distance from pole to equator. Both units have the advantage of universality (at least for users on this planet), but the disadvantage of scale (it's hard to find a measuring tape long enough to stretch from pole to equator).
Both units are equally (im)practical, but the metre has the (rather arbitrary) "advantage" of using base 10, where the nautical mile uses base 60. That's great if you want round numbers for your conversion factors when handling derived measures (as long as you also use base 10 in all your other dimensions, such as time or mass), but terrible if you want rational numbers for the results of simple arithmetical operations. The price we pay for using decimal is the proliferation of decimal
places, even for simple fractions like 1/3.
The metre and the nautical mile are both equally arbitrary, and both based on physical science - indeed, they are both based on the
same bit of physical science (the circumference of the Earth). But only one is an SI unit. It would be absurd to say "Physical science is based on the nautical mile"; it's obviously the other way about. It's exactly as absurd (and for the exact same reason) to claim that:
Physical science is based on Systems International.
SI is based on physical science - but it is in no way special in that regard; ALL metrologies in human history have been based on physical science.
* Such as the system the Americans call "English" or "Traditional", and the English call "Imperial".
Moreover, although the box had an x in the top right, clicking it did not make the popup go away. I had to do other shit to get out of the doom loop.