A fixed packing length is set. This is necessary with pre-printed foil. However, it also leads to lower film consumption and shorter packs with transparent film. The pack length is defined according to the longest product. This means that for the longest product the package is very tight and for the smaller products the package will always be a little longer.
With variable package length, the product is always longer due to the safety allowance.
The infeed belt is divided into compartments with blue markings. The product must be placed in one compartment. The machine does not have to correct because all products are at the same distance.
On a machine with box-motion system and variable length, it may happen that a distance is corrected on the feed belt and the welding process is not yet completed. This leads to the welding process being interrupted. In addition, the output is reduced if the distances are very different or very large.