[quote=@Memory]
<Snipped quote by Yatagarasu>

*Holds the handle of my magnifying glass against my cheek*
So in other words, we need to be able to recreate the entire spectrum of elements based on whatever base unit we pick.
[/quote]

That's a way to think of it, but it's not the reason, directly. And things get messier with some systems; we're lucky that we only have to deal with a common periodic table right now.