Abstract: A four-sided seal packaging machine having a side sealing unit, an end sealing unit, and an end cutting unit. The side sealing unit has a frame work, a first pair of cooperative sealing members to seal a first longitudinal edge of a package as the package is formed and a second pair of cooperative sealing members to seal an opposing longitudinal edge of the package. The first pair and the second pair of sealing members are mounted independently of each other to the frame work and each pair has a respective adjustment for adjusting the extent of compression together of the members of that pair independently of the other pair. The machine is well adapted for enabling self-validation, providing reliable high integrity seals.