A graph without units gives imagination permission to exaggerate.

Without units, a line going up is pure suggestion. It could be a doubling or a rounding error, and the reader’s imagination fills the gap, usually generously and in the direction the presenter wants. The shape does the persuading while the magnitude stays conveniently unstated.

When a chart moves you, check that you know what is being measured and in what quantity. If the axis is unlabelled, withhold the reaction until you have the number. And label your own charts fully, even when the shape alone would be more impressive.