hectogram, hundred grams, (kokuji)
瓸 is a Japanese-made kanji (kokuji) that represents a metric unit of mass: one hectogram, or one hundred grams. Its meaning is purely quantitative, with no abstract extensions.
瓸 is a modern kokuji created in Japan by combining 瓦 (used in many metric unit kanji for mass) with 百 (hundred) to represent one hundred grams. It has no ancient historical origin.
瓦 often appears in kanji for metric weights, and 百 means one hundred. Together they form a hundred grams: a hectogram.
For ヘクトグラム, the reading is simply the loanword 'hectogram' written in katakana. Think of the 百 inside 瓦 as a hundred grams, and say 'hectogram' to recall ヘクトグラム.
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