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 disabled, the correction will not be reversed and will not be adjusted to the scope declination.

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.