Weapon Class is used to overcome an opponent's Armour Class and the lower the WC , the better. Improvements to WC are listed with positives being improvements (-WC bonus makes your chance to hit LOWER).
The formula to calculate Wc is:
class Wc minus THAC0(STR) minus weapon Wc minus level minus 1 every 6 levels
Where
Weaponless attacks like the four combat skills clawing, flame_touch, karate and punching have also a Wc .