Where are the rules for tracking damage?

Question

A few weeks ago I had asked a question which dealt with an Eidolon losing HP when they get some distance from their summoner. The answer to that question had me find out that I might have been tracking damage wrong the entire time I have been playing d&d based games.

Does anyone know where I can find specific rules for how to track damage? I looked at the glossary in the core and was unable to notice anything. What I have been doing is keeping track of the damage taken (both lethal and non) and comparing it to my current max hp. Im looking for pathfinder specific as its the only variant Im playing right now.

Answer 1

Combat > Damage

Damage

If your attack succeeds, you deal damage. The type of weapon used determines the amount of damage you deal.

Damage reduces a target’s current hit points.

^{(emphasis mine)}

Note also Combat > Hit Points:

Hit Points

When your hit point total reaches 0, you're disabled. When it reaches –1, you're dying. When it gets to a negative amount equal to your Constitution score, you're dead. See Injury and Death, for more information.

These thresholds at 0, −1, and −Constitution make no senses if you tracked damage taken as a positive number; you instead track current HP, a value that you subtract any instance of damage taken from.

Finally, Combat > Nonlethal Damage > Dealing Nonlethal Damage

Dealing Nonlethal Damage

Certain attacks deal nonlethal damage. Other effects, such as heat or being exhausted, also deal nonlethal damage. When you take nonlethal damage, keep a running total of how much you've accumulated. Do not deduct the nonlethal damage number from your current hit points. It is not "real" damage. Instead, when your nonlethal damage equals your current hit points, you're staggered (see below), and when it exceeds your current hit points, you fall unconscious.

^{(emphasis mine)}

Here we see that you are running nonlethal damage correctly, but see how it is explicitly contrasted against “real” damage which does reduce current hit points. Again, the thresholds (equaling or exceeding current HP) only make sense if current HP is going down while nonlethal damage is going up (so they can meet and cross).