My really old , expensive one. A 20" Keuffel & Esser Co. engineers rule (USA), # 4053-5. From what I can find my example was made between 1922 and 1925, but, I'm no expert.
Has a straight edge ruler - inches on one side, mm on the other. Solid mahogany with some sort of white plastic reading surface (celluloid?). Discolored, but I don't dare touch it with cleaner. Being my longest one the numbers are easier to see and accuracy better between digits.
Missing the cursor - from what I can gather parts are NOT cheap! I keep it in a cardboard tube mailer for storage, hoping to find the parts for it someday.
Update: I think I found a proper cursor for $35, and one is selling on ebay starting at $125 (supposedly a rare one)!
And a K&E slide rule manual, again really hard to find these days. After 2 years of searching I found this at a used book sale for $1.