*This applies to PhotoModeler Pro 3.0 only. If you are using early versions of Pro 3.0, the confusion here normally arises because you are trying to reference Curve Helper points on to a third photograph. Pro 3.0g has a warning message on this issue, but if you are using 3.0b through 3.0f it can be confusing. Curve Helper points are created when you mark and reference at the same time with the Reference/Curve Helper turned on. These points are intended for curves only and can be marked on only two photos. If you wish to use the Reference Helper and not mark Curve Points (X with small c) so they can be referenced across multiple photos, do not mark new points during referencing. Instead, mark the points on all the photos first and then reference them with the Reference Helper line turned on.