Rare, archaic term for a paperweight. In modern Japanese, 文鎮 (ぶんちん) is the standard word.
Among the old calligraphy tools, there was a paperweight called 卦算.
The derivation is uncertain; the kanji 卦 (divination sign) and 算 (calculate) may relate to its use in weighing or fortune-telling contexts, but the exact origin is unclear.