ADAMSATOR

Your finger is the stylus

Choose a numbered tooth and slide in the direction shown above the tracks. For addition: red goes up, cream goes down. For subtraction: red goes down, cream goes up. Move to the end of the straight track; going around the hook is optional if you enjoy the traditional movement.

Use the two-position addition/subtraction switch below the tracks to change modes without changing the total. In subtraction mode, choose Set starting number to use the usual addition strokes: select a tooth and move it in the direction shown above, using the hook if you wish. Then choose Done · subtract. The current total is retained when you enter this mode; your strokes add to it. There is no automatic clearing. Undo reverses a completed stroke.

An arrow in a result window means another carry or borrow is needed. Select zero in that column and move the red tooth to the far end (or around its hook). Repeat for any further arrows. Carries never run automatically.

Pull the silver bar upwards to clear. Release before reaching the end of a track to cancel a stroke. Undo reverses one completed stroke or clear.

Keyboard: focus a column, type a digit, then press the arrow key in the direction shown. Focus the clearing bar and press Enter to clear.

This first version handles non-negative integers in the range 0–999,999. Going outside that range shows a warning; use Undo or clear.