Coordinates of two points—slope m (undefined if vertical line).
Slope = (y₂ − y₁) ÷ (x₂ − x₁). If |Δx| is essentially zero, slope is undefined and the page shows a localized message instead of dividing by zero. Coordinates accept a comma as decimal separator.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.