Appendix: Playing Octas in Decimal

You want to play Octas in decimal? You utter Barbarian!!

Octas isn't just a funny name. The game was developed to play in octal (numeric base 8) using a pair of 8-sided dice.

The game-as-presented is a bit of a compromise on the original concept, using octal (8-sided 0-7) dice but converting to decimal strait after DD or +DD dice rolls via a quick multiplication on the 8-times-tables. All the numbers used in the stock rules are presented in decimal.

The dice were actually developed first, because I made them as a 3D metal-printing demo project and didn't want to spend $100 printing something 'normal' I can buy in a shop for under $10. Then people kept asking me what game they were for, so I wrote one!

Plus I like the octal numeric system, it is probably the only serious contender against base-12 for an actually-good human-use-range numeric base, and for me the particular pros of octal, specifically around binary computers, outweigh the similarity-numbered pros of base-12. I'm an IT person by trade, so obviously I favour the computer-centric model. YMMV!

However, the game-concepts play fine in strait-decimal too, using a pair of 10-sided dice (often called 'percentile dice'), with just some minor adjustments.

10-sided dice.

Some D10s for decimal play

Above: the two on the right are ideal: single digits with something differentiating them (the colour of the numerals in this case). This is because Octas (Decamas?) doesn't only use the dice as a strait two-digit roll, so the X0 dice on the left can add confusion to non-DD rolls.

If using 10-sided dice, you don't actually change much:

You can't use characters from 8-sided-dice Octas mixed with those from 10-sided-dice Octas as the number ranges don't line up: 24 in octal is not the same number as 24 in decimal - they just use the same symbols, but the 2 is x8 in octal and a x10 in decimal.

In decimal, characters will be a little more powerful in stats simply because the dice that generate those stats can roll higher numbers. Of course their opponents will also be equally more powerful, so that balances out.

Probability changes a little too, as rolling a 0 on an 8-sided dice is a 1-in-8 chance but on a 10-sided-dice is a 1-in-10 chance, so expect skill progression to be a little slower, as you will get learning experience results less often on DD dice-rolls.

The biggest changes are that 9's are now the significant high number on dice rolls instead of 7's and a number of roll/comparison tables need to be altered to account for the wider number spread of numbers across 0-99:


Anywhere a roll of 7 is explicitly specified, it is now a roll of 9

Anywhere a roll of 7X is explicitly specified, it is now a roll of 9X

Anywhere a roll of 77 is explicitly specified, it is now a roll of 99

Character Creation.

The character stats start with 10 points each, and has a pool of 40 points to distribute.

Starting-skills are still rolled at +D+1, but now this has a range of 1 to 10.

Starting-weaknesses are now rolled at 2D-20 for a range of -2 to -20.

What Skill-levels approximately mean requires a new table with slightly stretched values to account for the wider number range between 00 and 99:

Score Meaning
below -10 Unbelievably incompetent
-10 to -6 Complete klutz
-5 to -1 Accident-prone
0 No notable ability
1 Picked up a few simple tricks
2 to 4 Knows how little they actually know
5 to 7 Barely capable
8 to 11 Novice
12 to 24 Competent
25 to 49 Expert
over 50 Master

The Language Fluency table likewise needs a little stretch:

Score Meaning
negative Worse than no ability. Will probably insult someone, or worse!
0 No ability
1 Knows a few words
2-4 Can barely understand or be understood
5-9 Can get by for day-to-day stuff
10-19 General competence
20-39 Educated
40+ Eloquent, including accent-free for non-native languages

Negative language starting-scores for making weaknesses out of Trade-lingua and Dæmonic are rolled 2d-20 for a 2-to-20 results range.

Instant Backstory: Re-roll 8's and 9's, or make up two extra rows to suit yourself!

Skill Checks (Game Master)

Difficulty modifier table:

Difficulty Modifier
Trivial +50
Easy +25
Simple +12
Normal 0
Challenging -12
Hard -25
Onerous -50

Opposed (Game Master)


Movement (Game Master)

Base movement table (humans and other species) unchanged.

Unencumbered speed is calculated as base movement multiplied by the high digit of the Current-strength score, or by 1 if there is no high digit.

Encumbrance table for land/water is now:

Carried Weight (in blocks) Effect
Up to half of strength x 10 Normal movement speed
Half to equal to strength x 10 Half movement speed
Greater than strength x 10 Cannot move!

For air the thresholds remain the same, encumbrance at twice strength, and over-encumbrance at four-times.

Close Battle (Game Master)

Defender Attacker Result Nomenclature
0 1-8 Automatic Miss by attacker Unlucky miss
9 1-8 Automatic Hit by attacker Lucky strike
1-8 0 Automatic Miss by attacker Lucky block
1-8 9 Automatic Hit by attacker Unlucky strike
0 0 Automatic Miss, weapon dropped Fumble
9 9 Automatic Hit, weapon dropped Lucky fumble

Basically, look out for 0s and 9s on these rolls, and apply the above table.

Ranged Attacks (Game Master)

Defender Attacker Result Nomenclature
0 1-8 Automatic Miss by attacker Unlucky miss.
9 1-8 Automatic Hit by attacker Lucky hit
1-8 0 Automatic Miss by attacker Lucky miss
1-8 9 Automatic Hit by attacker Unlucky hit
0 0 Automatic Miss, weapon jam Jam
9 9 Automatic Hit, weapon jam Lucky Jam

Area-effect Ranged Weapon (Game Master)

Defender Attacker Result Nomenclature
0 1-8 Automatic Miss by attacker Unlucky miss.
9 1-8 Automatic Hit by attacker Lucky hit
1-8 0 Automatic Miss by attacker Lucky miss
1-8 9 Automatic Hit by attacker Unlucky hit
0 0 Automatic Miss, attacker takes all damage Blow-back
9 9 Automatic Hit, attacker and defender share damage Blow-out

Some things never change.

The game is called Octas, so the number 8 is still going to feature quite a bit, even when playing in other numeric bases, just not where it will have much effect on the ease of game-play. Decimalisation is mainly focused around the use of 10-sided dice, and the related maths, so things that generally don't involve the dice in a significant way are left alone.

Some things that are explicitly not changed:

Fractional units.

Coin is still divided into 8ths. This has actual-world-related reasons - some old types of coin did get cut into 8 segments to make a smaller denomination, which was often accepted (mainly because at the time it was the weight of gold/silver in the coin that had value, not so much the coin itself). It is easy to accurately cut a disk into 2, then 4, then 8 (by 16, you are getting a bit small!). Not so easy to do 6ths or 12ths, due to the need to cut accurately into 3rds eventually, or even worse, 10ths due to the virtually-impossible-without-measuring-equipment 5-way split.

Measurement, both Lengths and Blocks, are likewise also still divided into 8ths. The game explicitly avoids fractional units as more than a flavour component, so continuing to use 8ths here isn't really an issue.

As much as the Ancient Romans loved counting whole things in decimal, they actually used 12ths for fractions, so having different numeric bases above and below the unit-value is not even unprecedented.

Rolling 1/8 fractions on a 10-sided dice.

This will rarely occur but if it does, such as when rolling the fractional parts of height and weight for a character, you can count 8 as a whole 1 (8/8ths) and 9 as 1+1/8 and bump your whole-number value for that stat by 1 with the fractional value being 0 or 1 respectively.

Or if that doesn't suit the situation, just re-roll any 8 or 9 results.

All your base are belong to ... well, numbers are a public resource, really!

Playing Octas in other numeric bases that are also not Octal!

Due to being developed in octal, but with play by decimal-users in mind, the Octas system is relatively numeric-base agnostic, within a modest range.

Dozenalists should feel free to use this appendix as a guide to adapt Octas to base-12, where 10 is the number after ↋, and a pair of dodecahedral dice numbered 0-↋ might be used. Just look at how octal was converted to decimal in this appendix and do it for dozenal instead. The number range (0-143 decimal) is getting a little unwieldy, but I feel that way about the decimal 0-99 range too, yet billions of people manage it daily, so be you! Just be aware your chances of rolling zeros (a significant thing in Octas) are quite a bit lower, slightly less than half!

Base 12 is a particularly good base for simpler human use, but once you get computers, it suffers the same binary conversion issues as base-10. It has one big advantage over base-8, namely whole-number division by 3 (and 6) but also one equally big disadvantage, in that sooner or later you have to divide that three, which is quite difficult to do accurately in the physical world: try folding a piece of paper into 3 equal pieces, without a ruler or guides, or cutting a pizza into three or six equal slices - you can do it, but it takes a lot of effort (or much-repeated practice) to judge it right! Sub-groups of already-discrete things, like eggs in a box, are far easier, of course.

It would be rather cool to see an origional in-the-spirit-of-Octas TTRPG from the Dozenalist community, actually. While you can squeeze Octas rules into base-12 as discussed above, writing something new and explicitly tuned for that number range is almost-certainly going to be better. And in the end, the more the merrier!

Senarians could likewise adapt the game to base-6, using cubic dice, though you will need to get hold of a pair numbered 0-5 (or just remember that six dots is a zero, or scratch-off/paint-over the symbol-6's stalk if it is a dice numbered in hindu-arabic glyphs). The numeric range (0-35 decimal) might be getting a bit tight there, though is probably still workable. Chances of rolling zeroes is a good bit higher in this base (almost double!), so expect skill-progression to be fast, maybe too fast!

I quite like base-6 as you can count it on the fingers of one hand (closed hand for zero, and count to 5 with fingers) and then use the other hand for a second digit. Zero is explicitly included, making it a positional counting system right there on the ends of your arms, right up to 55 (35 decimal)! Lack of a whole-number division-by-4 is probably its only drawback, though at least that still results in a very simple fraction (1½).

Quaternians, sorry. I actually tried this one myself and base-4 is just too small for human use. Numbers in the common-use range quickly blow out to unmanageably long strings, and the numeric range from two 4-sided dice (0-15 decimal) is too narrow for the Octas rules to work effectively within. You could use three 4-sided dice for the same 0-63 (decimal) range as in original Octas, but replacing a 2-dice system with a 3-dice system means you have to pretty-much develop an entirely new game anyway.

Base-4 has some quite interesting mathematical attributes, but trying to create an Octas-like game in it demonstrated the base's unsuitability for general human use very quickly.

Vigesimalists (!!) I am not even going to try to work out how to number those dice! Base-20 on the Octus system is going to give you a number range from 0-399 (decimal) from two dice, and worse than one-sixth the chance of rolling a zero! I doubt that is really useful, and you would probably be better off adapting a rule-set designed for a single 20-sided dice.

Sexagesimalists, 60-sided dice are an actual thing you can buy, even based of a semi-regular solid shape, so the dice are genuinely 'fair'. But you just don't need two dice at this point! At 0-59 (decimal), a single dice covers almost the entire range of an octal DD dice, but the Octas rules are very explicitly designed for two dice and takes advantage of a number of different ways two dice can be used together. Again, adapting a single-dice D20 game, or a strict-D100 system, is almost certainly the way to go.

Hexadecimalists, go home! We all know you are converting to base-4, doing the maths in that, then converting back to base-16 at the end! And since our dimension lacks any 16-sided (semi)regular solids to base the dice off, hexadecimal dice have to be made in the same awkwardly-rolling manner as decimal dice (if you want 'fair' ones), or not be truly symmetrical (if you want better-rolling 'round' ones that won't be properly 'fair').

The only notable thing about hexadecimal is that it very neatly packs 2 digits exactly into 8-bit bytes which are standard on modern computers. Though even here it is mostly used as a human-readable way to represent binary strings, rather than as a numeric system in its own right. Hex colour codes are really the only common actually-numeric use, and no human normally does even the simplest mathematical operations on those.

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