Rules of Thumb
Given that plugging the combat formula into a calculator whenever engaged in combat may be a bit much, the following general rules can be learned and relied upon
The real result can range from about 2/3rds to 4/3rds what the combat information table predicts.
A predicted 6 damage can result in from 4 to 9 damage.
A predicted 1 damage can result in at most 2 damage.
A predicted 10 damage can potentially result in 6 minimum.
Units gain damage at odd amounts of health; a 9 hp unit fights as though it were full strength.
The guaranteed kill ratio is at about 2.7x strength; the unit will do 10 damage and generally take at most two.
Attack melee units with ranged, and ranged units with melee.
Attack and destroy naval units with naval units; do not receive counterattacks from naval units.
If both combatants are predicted to die, the attacker must end up with more hit points to survive.