On pier flip allows to define how the correction will be reversed. By default, Reverse X.

 To test full frame guiding with the telescope simulator, disable pier flipping. When pier flip is set to do nothing, the correction will not be reversed.

If the X axis corresponds to the right ascension axis of the mount, choose the “Reverse X” option.

If the Y axis corresponds to the right ascension axis of the mount, choose the “Reverse Y” option.

 Some mounts like Software Bisque requires to reverse both axes after pier flip. With any model of Software Bisque mounts choose "Reverse both" option.