Reversible pattern or not

You can optionally choose to make a reversible crochet pattern. With a reversible pattern, the back of the work shows the same design as the front, but with the colors reversed. This is achieved with negative stitches. (If this is new to you, a brief internet search will tell you all about the technique.)

Because CromoViewer calculates where the negative stitches go from the original pattern, the designer doesn't need to prepare anything — making a pattern reversible is entirely your choice as the crocheter.

The CromoViewer properties dialog has a toggle to enable negative stitches; once enabled, they're added to the pattern and shown with a − sign in the chart.

Slanted stitches and reversibility

A reversible pattern only works well if the design doesn't use slanted stitches.