A mechanical analog calculator; the Japanese term 計算尺 is far more common. This loanword is rare and mostly used in historical or technical contexts.
See also: 計算尺
昔の技術者はスライドルールで計算していた。
Engineers in the old days used to calculate with slide rules.
Variant spelling with an interpunct; less common but still encountered.
Loanword from English 'slide rule'.