I have also see some weapon calculations that confuse me

specificaly the strenght 0.5

and one another that had something like 4/25

i dont remember the latter but i think it was something like that

These appear in the bootypedia at the weapon page

Some weapons have bonuses to Hit % and/or Damage Increase.

Those that say "Skill:" use that particular attribute equation to boost the Hit %.

Examples:

Machete - Base Accuracy: 80%, Skill: Melee/2+50 means whatever the Soldier's Melee Skill is (say, 80) divided by 2, plus 50 for a total of 90 times the weapon's base Accuracy 80% for a boosted Hit % of 96%.

Dagger - Base Accuracy: 75%, Skill: Melee means whatever the Soldier's Melee Skill is (again, 80) for a total of 80 times the weapon's base accuracy 75% for a Hit % of 60%.

So essentially, the Machete is better for low Melee Skill soldiers than Dagger, but high Melee Skill soldiers are better using Dagger.

For POWER bonuses, particular attributes are equated to boost the damage of a weapon.

Examples:

Machete - Base Damage: 20, POWER Bonus: Strength*0.2+Melee*0.1 means Soldier's Strength (say, 55) multiplied by 0.2 plus Soldier's Melee Skill (again, 80) multiplied by 0.1 and the sum of these two is added to the Base Damage (20) for a total of 39 damage.

Dagger - Base Damage: 20, POWER Bonus: Strength*0.2+Melee*0.2 means Soldier's Strength (again, 55) multiplied by 0.2 plus Soldier's Melee Skill (again, 80) multiplied by 0.2 and the sum of these two is added to the Base Damage (20) for a total of 47 damage.

So again, Machete is better suited for low Strength/Melee Skill Soldiers, as Daggers are better for high Strength/Melee Skill Soldiers.

Formula functions are great as they can be made to do them automatically (with like Excel, Calc), but generally weapons with high base accuracy and limited Power bonuses are best for unskilled soldiers, but best to find the highest attribute(s) of a Soldier and try to find a weapon(s) that fits best.