Eutectoid steel (0.76 wt% C) is austenitised above 727 °C, then quenched and held at a constant temperature. Drag the dot anywhere inside the diagram — its time (x) and temperature (y) tell you what fraction of austenite has decomposed into pearlite, and whether it is coarse or fine.
Drag the dot anywhere on the diagram. Switch the toggle above the plot to Heat-treatment path to draw an A→B→C profile and scrub a playhead along it.