Put a gap in an axis

When plotting scientific data, you will often want to create a discontinuous axis (with gaps).

Creating a gap in an axis

To create a discontinuous axis with Prism requires three steps.

1.	Double-click on the axis to open the Format Axes dialog. In the Gaps and Directions section, you can choose either a two-segment (one gap) or three-segment (two gaps) axis.

Set the length and range of each segment. For each segment, set the range and length (as a percent of the total length of the axis). You can also drag the segments to the size you want. Click on the axis segment to select it. You'll see selection knobs at each end. Drag the knob just to the left of (or below) the gap to change the position of the gap along the axis (make one segment larger, and another smaller). Drag the knob to the right of (or above) the gap to widen or narrow the gap itself.

3.	Format major and minor ticks for each segment. You can choose the spacing and properties for minor and major ticks separately for each axis segment.

Examples of discontinuous axes:

Double-click on the X-axis to open the Format Axes dialog. In the Gaps and Direction section, choose Two segments. Then follow the tips below to match the sample graphs.

Set the range for the left segment to 0 to 15, and the length of the segment to 67% of the total. Set the range of the right segment to 15 to 50, and the length of the segment to 33% of the total.

Because of the change in scale, the linear regression line appears to have two slopes. In fact the mathematical slope is identical everywhere, and the line was created by a single analysis of all the data. The slope just appears steeper in the right half of the graph because the time scale is more compressed.

The first number on the X-axis is "0". This was created by substituting a additional tick label at X=-9 (one log unit less than the lowest concentration used).

Set the range for the left segment to -9.5 to -8.5, and the length of the segment to 12% of the total. Set the range of the right segment to -8.5 to -2.5, and the length of the segment to 88% of the total.

Set the range for the left segment to 0 to 24, and the length of the segment to 50% of the total. Set the range of the right segment to 48 to 72, and the length of the segment to 50% of the total. The line was drawn by linear regression, which automatically skips over the axis gap.