In order to have full control over the way that the labels are displayed it is possible to define a callback function that will be applied to all labels. The callback function will be called with the label as the only argument and should return the value that will be displayed in the graph. This could for example be used to turn seconds (used to position data points) into hour and minutes on the scale. For further reference see the two methods: Graph::SetLabelFormatCallback(); and Graph::SetLabelFormat();