Interactive sliders & knobs

Any plain numeric definition can become a draggable slider: open its cell menu and choose "Add slider". Drag the knob and every downstream cell — results, checks, plots, diagrams — recomputes live, so you can feel how an input drives a design. It is the fastest way to explore a what-if. Pair a slider with a check and you have a goal-seek knob: drag until the check turns green.

Sliders turn a static calculation into a tiny interactive model — one of the most useful habits in NapkinCalc.