If I'm making an image with a standard set of seven dice, all showing as having rolled the lowest possible result, I obviously want to have that be 1 for six of them, but what should I use for the percentile one? 00 or 10? Is there ever any circumstance in which it's rolled on its own?

It's system dependent.

Let's see, the "percentile die" is a combo of two dice: the one numbered 00 to 90 (d10×10) and the one numbered 0 to 9 (d10) and then summed up.

Now, it depends on the system how to read them, as there is no system-agnostic decision on the one case we are most interested in:

The system determines if "00, 0" is read as 100 or 0 (just like it decides if "0" is 10 or 0). Usually it does so either in form of text or by providing tables — if there is a 0 column/row or a 100 one.

The "00, 0" = 100 is the more widespread choice, as it generates 1–100. Among others, this is used for example in D&D and Hackmaster¹ interpretation (unless one interprets "00, 0" as 10 and "90, 0" as 100).

The "00, 0" = 0 is the standard interpretation for games that use 0–99 tables. Among these is one edition of Pendragon.

^{1 - If you ever wanted to learn how to pray to and kiss your dice, grab a 2001 4th Edition Hackmaster Player's Handbook, Appendix L page 347–350.}

Be easy on yourself

The otherwise lowest value ignoring the "00, 0" outlier is "00, 1", a 1.

It depends on the conventions you use for reading your dice.

To roll a number with a 1% chance of getting each number in the range you need to have a percentile dice (d% or a nominated d10*10) and a d10 dice.

There are broadly three ways to read these dice, each with their own set of conventions.

Method 1 - read the d10 as 0-9 and the percentile dice (d% or d10*10) as 00, 10, 20, ... etc

The natural sum of the two dice then gives you values from 0 - 99.

In this case the smallest value the dice can give is 0.

Example Calculations:
beginarray
hline
textPercentile Dice (d%) & textd10 dice & textresult \ hline
00 & 0 & 0 + 0 = 0 \ hline
00 & 5 & 0 + 5 = 5 \ hline
20 & 0 & 20 + 0 = 20 \ hline
90 & 1 & 90 + 1 = 91 \ hline
90 & 0 & 90 + 0 = 90 \ hline
endarray

Method 2 - read the d10 as 0-9 and the percentile dice (d% or d10*10) as 00, 10, 20, ... etc, with the exception that a combined roll of 00, 0 is relabelled as 100

With this method we've introduced an exception for a roll of 00, 0. In particular, we've removed the lowest value from the previous set of sums.

Aside from the exceptional case we sum values on the dice as in method 1.

So now we get a range of 1-100 on the dice, with the lowest possible roll being 00, 1 this gives a value of 1.

Example Calculations:
beginarray
hline
textPercentile Dice (d%) & textd10 dice & textresult \ hline
00 & 0 & 100 \ hline
00 & 5 & 0 + 5 = 5 \ hline
20 & 0 & 20 + 0 = 20 \ hline
90 & 1 & 90 + 1 = 91 \ hline
90 & 0 & 90 + 0 = 90 \ hline
endarray

Method 3 - read the d10 as 1-10 (assigning the 10 to 0) and the percentile dice (d% or d10*10) as 00, 10, 20, ... etc (ie the same way as method 1)

In this method we do a straight sum of the two dice to get a read.

This gives us a range of possible values of 1 - 100, with the lowest value being 1 (on a roll of 00,1)

Example Calculations:
beginarray
hline
textPercentile Dice (d%) & textd10 dice & textresult \ hline
00 & 0 text (ie 10) & 0 + 10 = 10\ hline
00 & 5 & 0 + 5 = 5 \ hline
20 & 0 & 20 + 10 = 30 \ hline
90 & 1 & 90 + 1 = 91 \ hline
90 & 0 & 90 + 10 = 100 \ hline
endarray

Summary

One thing all three methods have in common is that a roll of 00 is the lowest you can roll on the d% (what you and I are calling the percentile dice).

Importantly this does not mean that a roll of 00,0 is always the lowest, just that rolling a 00 on the percentile dice participated in the lowest roll in all three methods.

It is also important to point out that I'm talking about numerically lowest, not the "best" or "worst" result. What is the best or worst is entirely system dependent.

The lowest value on the tens die is 00.

The tens die (00, 10, 20, etc) was invented for the sole purpose of making it easier to roll percentile dice. I'm not aware of any RPG which uses it on its own. That's not to say that one might not exist somewhere, or that someone could not make one, but it's not at all common.

The lowest value it can roll is 00, since in combination with the singles ten-sided die it can roll results like 01, 02, 03 and so on, all of which are lower than any value with 10 showing on the tens die (11, 12, 13, and so on).

In D&D, at least, 01 is the lowest and 00 counts as 100.

Naturally this could vary in other games, but in every edition of Dungeons & Dragons that I'm familiar with, percentile dice are rolled in this manner. Most roleplaying game players today are familiar with percentile dice from Dungeons & Dragons, particularly newer editions of that game, making this the closest thing to a standard. The term "percentile dice" is also particularly used by AD&D and later D&D.

D&D 5th edition Player's Handbook, p.6:

Percentile dice, or d100, work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice numbered 0 to 9. One die (designated before you roll) gives the tens digit, and the other gives the ones digit. If you roll a 7 and a 1, for example, the number rolled is 71. Two 0s represent 100. Some ten-sided dice are numbered in tens (00, 10, 20 and so on), making it easier to distinguish from the tens digit and the ones digit. In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.

D&D 3.5 Player's Handbook, p. 5 is almost identical:

Percentile dice work a little differently. You generate a number between 1 and 100 by rolling two differently-colored ten-sided dice. ... A roll of 7 and 1, for example, give you a result of 71. Two 0s represents 100. Some percentile show the tens digit in tens (00, 10, 20, etc.) and the ones digit in ones (0, 1, 2, etc.). In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.

AD&D 2nd edtiion Player's Handbook, p. 11:

When the rules say to roll "percentile dice" or "d100" you need to enerate a random number from 1 to 100 ... Rolling them together enables you to generate a number from 1 to 100 (a result of "0" on both dice is read as "00" or "100").

AD&D 1st edition Player's Handbook, p. 9:

Furthermore, fighters with an 18 strength are entitled to roll percentile dice in order to generate a random number between 01 and 00 (100) to determine exceptional strength

The adjacent table notes that the lowest possible exceptional strength is 18/01 and the maximum human strength is 18/00, suggesting that even when written "00" it is considered to represent 100.

Your best option is to look at other dice with artwork and go from there. A design or pattern would fit any result. A single die type can easily be customized with one unique face design, but a full polyhedral set of 7 is tricky.

See my short description below about percentile facing results:

Percentile is either 2xd10 (0-9 faces) or d10 (0-9 faces) + d10 (00-90 faces), with a rarely used d100 (1-100 faces)

Results are 1-100% but the die face determines a high or low result.

0 can be highest or lowest depending on the other die’s result

• 00 (lowest face) + 0 (highest face) = 100


• 10 (low face) + 0 (highest face) = 10


• 00 (lowest face) + 1 (lowest face) = 1

d10 (ones’ place faces) = numbered 0-9 result = 1-10 (1 low : 0 read as 10 high)

d10 (tens’ place faces) = numbered 00-90 result = 00-90 (00 low : 90 high)

(D&D5e PHB pg. 6)