Experiment: Arma Obscura – Weapons Defined as Nomograms

Arma Obscura is a brief experiment on an unusual way for defining weapons and equipment for RPGs and Dungeon Crawlers. Instead of defining them as a collection of static parameters and/or modifiers, items are defined as interactive Nomograms, which can pack the interrelation of a bunch of variables in the 2D space of a card and can be used by simply tracing a line through the known variables and choosing the desired outputs. To do so, players would use a transparent ruler or guide with just one flat thin line at the bottom side.

I like the idea of players finding a new weapon and playing with it with their rulers while trying to unravel its potential and decipher which would be the best way to use it in the current circumstances of the game.

How it works

You take the card and using your ruler, you trace a line choosing the results that you like the best within the constrains that are determined by the game state, such as distance to an enemy or PC stat value. The correct value is the one which the line touches (considering its box), if the line touches 2 boxes of the same value, the one that is touched closer to the bottom is considered the right one.

You can download a black and white printable version of the card here:

The card

I would use the back of the card to plot the nomogram while I would keep the front for the art, the flavor text and a summary of the stats and features of the card. Right now I only just one card, just the back.

The example card, The Bow of Misery can cause up to 10 damage, hit from 2 to 7 tiles of distance and add piercing damage, stun or the possibility of choosing specifically which part of the body to hit.

In the way the variables are plotted, the closer to the target, the more damage and lower accuracy roll requirement and in general, the more accuracy, the less damage.

The Bow of Misery card back.

There are 4 types of variables in the card:


All the stuff that can come from the game current state. In the example is used for the distance in tiles from the PC to the target.

Playable Character Stats

The values that come from any of the stats of the player. In the example, it is used to mark the max charge of the shot as an expression of his Archery stat.

Dice Roll

Whatever value that is bound to rolling a dice. In the example, Accuracy will output the number that has to be reached by a d20 roll in order to hit the target.

Choice Outputs

Variables that are output from the decision of the player. If the line touches the container, then the output applies. In the example card we have:

  • Damage scale: from 1 to 10
  • Piercing +1
  • Stun +1
  • Hit Limb (short for ‘Aim for a specific body-part’)

Sorry for the shameless appropriation of the Yiddish alphabet, I didn’t want to clutter the card with icons and numbers or Latin and Greek alphabet could be taken as values or textual labels.

Practical Examples

Shot at Distance 3

Let’s assume that you are exploring that Dungeon and an enemy is spawned at 3 tiles of distance from your PC:

Just imagining the setup on a hex grid in a fantasy setting.
Thanks to dutchmogul for sharing the Elf Rangers and to onmioji for sharing the Winged Demon under CC0.

Then, you grab your ruler and use your Bow of Misery against him before he gets too close.

If you have maxed archery to 20 your range of options would be:

With inverse proportion you could choose between:

  • Damage: 5-9
  • Accuracy: 4-13 (85-40% chance on a d20)

Plus any or two of these possible bonuses:

  • +1 Piercing
  • Hit a Specific Body Part

Most valuable shot at the current distance of 3
(red line) would become available only once you level up Archery to 17 and it would be:

  • Damage = 9
  • Accuracy = 7 (70% chance on a d20)
  • +1 Piercing
  • Hit the chosen limb

But if the creature has just 4 HP and you want to make sure you kill it before it reaches you, you can decide to go for a certain shot and hit it for just 5 damage with an accuracy roll requirement of 4 (80% chance with a d20).

Shot at distance 6

Now, shooting with the same weapon at 6 rows of distance.

The available ranges would be

With inverse proportion you could choose between:

  • Damage: 1-5
  • Accuracy: 11-20 (5-50%)

Plus this possible bonus:

  • +1 Stun

The most valuable shot in this case would be questionable due to the chances of hitting.

  • Player could deal 2 of damage with a 50% chances of hitting (Accuracy 11) or even 3 damage with a chance of 45% (Accuracy 12).
  • On the other hand, the most damaging shot (red line) would impact for 4 damage plus cause stun, but with a hitting chance of 20%.

If you want to know more about it, there’s some grandpa’s chatter in the next page about nomograms and earlier iterations of the cards.

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