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> Instead, metric hectares and metric dunams were adapted to be metric

Ares (and therefore hectares) aren't part of the SI system, but they are original metric units -- an are is 10m×10m, hect- is the prefix meaning 100×.

The metric angular unit is a gradian. I've heard of it, as I read the whole manual when I first had a scientific calculator, age 11-ish, but I've never worked in a field where it's used.

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The International System of Units (what most people refer to as "the metric system") unit for angular measure is the radian.

Pedantically, the SI standard[1] defines the term "radian" as a "special name[] for the number one that may be used to convey information about the quantity concerned."

[1] https://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf

The gradian was the original metric angle unit, before it was replaced by the radian in SI because the powers that were decided that pi was more important than base 10, as the standard prefixes are nearly useless for angular measure.

In terms of circles, angles, and, well, geometry in general, it's pretty hard to argue against the claim that pi is more important than ten.

My mistake. I thought hectares predated their current size.

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