Specialties are beneficial effects that are present in every hero. Some specialties are not unique to a specific hero, an example is Dessa, Gunnar, and Kyrre, all three of them have the specialty of Logistics.
Specialties of Sorcery, Logistics, Offense, and the like have similar effects, that is, a 5% per level increase to the skills's percentage. To calculate for this type of specialty, you must get 5% of the secondary skill's effect and multiply it to the hero's level, then add to the skill's effect.
Formula = (.05*Secondary skill's effect percentage*Hero level+Secondary skill's effect percentage)
Example: Level 20 Crag Hack with Expert Offense.
.05*30*20+30 = 60, thus Crag Hack's army will deal 60% more damage. That means that he has gained a 30% increase to his Offense skill. It also means that he gained 30% more offense than any other character, aside from Gundula would have.