All charts require labels to convey their story accurately. Axis labels must accurately represent their scale. Indicating what data the chart represents as well as any units used to measure that data.

Category Axis Labels can help to illustrate how data is divided up by categories (for instance products, risk factors or time periods). You can modify what text appears on these labels using the LabelText property.

If you wish to customize the format of a single category or value axis label, select each cell within the worksheet data range connected to your chart that contains that label text, then type your changes directly in that cell. Your chart labels will automatically reflect these updates. Alternatively, the Formatter property allows you to create custom formatters and apply them globally across chart axis labels.
Axis Ticks

Tick marks generated by software are temptingly simple; yet careful consideration can lead to more refined appearance and enhanced reading experience.

Select a color for both major and minor tick label text.

Customise the spacing between major ticks.

Indicate whether each tick label will display a power unit.

Axis ticks are used to distinguish major units on an axis (category axes do not show minor ticks). Minor ticks subdivide the major ticks; one minor tick appears for every major division on an axis.

You can specify a custom space between major ticks to indicate the number of decimal places for numeric displays, as well as enable or disable an option to show percentage signs in value tick labels.
Labels on Transformed Scales

Labelling transformed scales is possible, although their format depends on the type of transformation used. To add labels, the labels function uses similar arguments as breaks() but returns a character vector rather than numeric data.

Empirical evidence generally supports fully labeled scales as having advantages over partially labeled ones, yet question designers should use their own evaluation methods to decide which approach is most suitable for their research design. Scale points play an integral part in this decision; often adjectives cannot be generated for more than 5 or 6 points along most continuum. Telephone interviews tend to prefer shorter scales so respondents don't need to listen through long lists before answering.

Consider whether the scale has a clear meaning for respondents. Verbal scales may be difficult for cross-cultural translation. Numeric scales tend to be better understood across cultural boundaries and may lead to greater reliability than verbal ones (Fowler 1995).
Labels on Discrete Scales

For discrete scales such as dates or compass bearings, it may be beneficial to demonstrate missing values as blank spaces. For instance, if the scale relies on dates or periods, an NA space should be added between every three decimal places so as to differentiate it from numeric values.

Also useful are other formats for numbers, such as label_numebr() to display comma-separated numbers or label_date_format() which displays dates in HH:MM:SS format.

Many functions support the label_scale() argument for scaling functions. Common examples are scale_color_gradient() and scale_fill_gradient2() which create color gradients from discrete colors; scale_size_radius() scales values in linestyle aesthetic to measure units; label_parse() creates expressions from strings while label_math formats mathematical values (see?plotmath for details); these functions may be used either before or after transformations.