TLDR: instead of tracking hp, make a box or circle for each HD a creature has and tick them off as the hits come in, rounding up or down to "5" per box.
Let's start with this - hit points (hp) is just a more granular way of representing hit dice (HD). In most old school games, creature HD come in d8s. An average roll on a d8 is 4.5. So 1 HD = 4.5 hp.
Weapon damage varies from d4 to d10, usually. The ranges, averages look like this:
- d4: 1-4, 2.5
- d6: 1-6, 3.5
- d8: 1-8, 4.5
- d10: 1-10, 5.5
Running encounters with hp is the norm that most of us have used countless times. If a creature has 7 HD (32 hp), we start with 32 and whittle it away as the hits come in. Let's say the damage done to a creature by a party over the course of a few rounds goes like this: 2, 9, 4, 6, 7, 1, 10! That's a total of 39, with the final shot getting in 7 points of "overkill" damage. That's all fine and good. Basic addition/subtraction math is pretty easy.
But why all this granularity? Is it for some notion of "realism" or to make things less predictable? Does it actually make the game more fun? Consider the following way of tracking things as the GM.
Same monster, same fight. The monster's HD are marked as bubbles like:
Monster: HD 7 OOOOOOO
As the damage comes in the bubbles get marked off as follows:
- 2 damage: no bubble is marked, but maybe a dot or tick mark is used to show a weak hit.
- 9: two bubbles gone! (10 tracked damage in bubble form /11 actual damage by weapons.)
- 4: another bubble (totals now 15 tracked / 15 actual)
- 6: one more (20/21)
- 7: one more (25/28)
- 1: none? one? This is the GM's call if their gut says they are running behind actual damage. Let's say none for argument's sake. (25/29)
- 10!: two (35/39) - the monster is defeated!