Disregarding Armor, resulting damage is calculated by multiplying the Base Damage, an absolute number, by the percentage coming from the Melee DamageAttribute.
The difference between Base Damage and Melee Damage is that only the latter can be seen ingame. This may lead to confusion of the player because it does not seem obvious that Melee Damage is not the only Attribute affecting the damage.
Higher Melee Damage does not necessarily mean higher resulting damage.
Ignoring armor, Weapons may deal different amounts of damage depending on where you hit a certain creature. For example, you only deal 20% damage against a Carbonemys' shell body part. Many creatures also take additional damage if you hit them in the head, with differing multipliers. However, the damage against the fleshy body of the organisms stays the same across all of them.
Weapon damage values
Against unarmored bodies, the damage weapons do per shot/attack is listed in the following table.
The Percent Torpor Gain is based on the % Melee Damage Attribute of both the weapon used, as well as the player using it.
For example, a Ramshackle Wooden Club with 120% damage will do a base damage of 6. With its torpor gain multiplier of 3.75, it will now do 22.5 torpor per hit.
Note: all values were taken from the raw damage values of the blueprints in the dev kit.
The minimum pulling time to shoot an arrow with a bow is 0.3 seconds and the maximum damage is reached after pulling for 1.2 seconds. An arrow's damage starts at 25% at 0 seconds, and increases linearly up to 100% at 1.2 seconds. Since an arrow can only be launched after 0.3 seconds, this means that the minimum damage of an arrow is 43.75%.
The only difference for slingshots is the minimum pulling time, which is 0.25 seconds, resulting in a minimum damage of 40.625%.
Since the Base Damage value can not be seen during gameplay, other methods are required to find out the exact numbers, such as in-game testing, receiving the values from the developers (like in Patch Notes 173.0), or by extracting them from the Dev Kit.
In v242.0 a server-option for displaying the dealt damage as a floating number (as known from RPG-games) was added. This mode is not enabled on official servers, but is always enabled for the damage dealt to the Training Dummy.