Captain Anorak's
Guide to Gaming
The Stepping Problem
A common probelm in RPG rules systems is that large steps exist
in things like difficulty levels. For instance,
in Call of Cthulhu Edn 5, a shooter with Pistol skill 40 and DEX 12
firing a .32 revolver has the following base hit chances at the
following ranges.
| Range (yards) | Hit chance |
| 0-2 | 80% |
| 2-15 | 40% |
| 15-30 | 20% |
| 30-45 | 10% |
| 45-60 | 5% |
Now, the change from 80% to 40% is a very big jump.
Why should the firer have an 80% chance to hit at 1 foot 11 inches,
but only 40% at 2 feet 1 inch? The answer is that the game writers
have tried to keep the system simple, so they came up with these
rules:
- Half-DEX in feet is point blank range (double hit chance).
- For each rangeband beyond the first, halve the chance to hit
(this pistol has 15 yard rangebands).
But with a little more thought, these large steps could be
eliminated. Suppose we make these changes to the system:
(1) Double weapon skills (so our skill of 40 now becomes 80).
(2) We give the weapons smaller rangebands and apply
a -10% penalty per full rangeband.
(3) A shot has a minimum 1% chance to hit up to the weapon's
maximum range.
If we give the pistol rangebands of 5 vards then we get this
pattern:
| Range (yards) | Hit chance |
| 0-5 | 80% |
| 5-10 | 70% |
| 10-15 | 60% |
| 15-20 | 50% |
| 20-25 | 40% |
| 25-30 | 30% |
| 30-35 | 20% |
| 35-40 | 10% |
| 40-max | 1% |
This has roughly similar hit chances, but there are never
catastrophically large steps over a difference of an inch -
such steps are never more than 10%.
Another dreadful example of stepping is MegaTraveller.
This game has huge stepping throughout the game system. For
example, on a successful hit, the damage inflicted is equal
to the weapon's damage multiplied by a factor dependent on
the number of points by which the roll was made (ie.
actual roll - target number) thus:
| Roll - target number |
Damage multiplier |
| 0 | x0.5 |
| 1 | x1 |
| 2-3 | x2 |
| 4-7 | x4 |
| 8+ | x8 |
Why should an excess of 7 be no better than one of 4?
It's almost twice as much. The rules could have been written
without stepping like this:
- If the excess is 0, halve the weapon's damage; otherwise,
multiply the weapon's damage by the excess.
This would have been no more complicated than the system used,
and would have involved rembering less, yet is would have resulted
in a system with less artifical results from stepping.