Rollable Tables - Help?

Ok, I'll admit up front my math skills are not the best. I am having issues understanding Rollable Tables. I want to create a Hit Location table for GURPS 4e. It is based on the following: Roll Location 3 - 4 5 6 - 7 8 9 - 10 11 12 13 - 14 15 16 17 - 18 So as far as I understand the instructions for Rollable Tables, each item on the above example with two numbers would have to be added twice or weighted (no sure how that works). However, what about the inherent probabilities of the dice themselves? GURPS 4e uses 3D6 so different results have different probabilities. How do you figure that into a Rollable Table?

I pulled this table for rolling 3d6 off the internet.  It matches what I expect, but I make no guarantees about reliability.  It's Saturday, I'm not going to be doing nCr or factorals on my day off. 3: 0.5% (actually 0.46, or 1 in 216, but rounded off for this table) 4: 1.4% 5: 2.8% 6: 4.6% 7: 6.9% 8: 9.7% 9: 11.6% 10: 12.5% 11: 12.5% 12: 11.6% 13: 9.7% 14: 6.9% 15: 4.6% 16: 2.8% 17: 1.4% 18: 0.5% (as 3’s note above)

EDIT - There's an easier way below, ignore this. Now, knowing the above and that the rollable tables need to be weighted to equal 100, you're going to have to give each entry a percentage value that includes some rounding as the "weight" so it adds up to 100. Since 3-4 equals a skull hit, I'd be inclined to give it a weight of 2 if I were going to make a rollable table. 5 for a face hit I'd give a weight of 3....and so on.  Make sure all of the table's entries add up to 100. In my GURPS game, I played around with making groin hits less common, and you can do that in the custom table easily enough too.  Heck, you can make a specific "vitals" hit if you get your table custom enough.

A few people beat me to it, but I think this may be a better solution than percentage since there is no rounding. 6 to the 3rd is 216.  Thats how many different combos there are. So you need a table with 216 entries.  I haven't used tables so I'm not familiar with them.  Weighting might be the thing to use, but I haven't tried it, so but for now it's 216 entries.  So for example the first 4 entries in your 216 table will be the result for the roll of 3-4.  The next 6 entries are for the roll 5.  and so on until you have entered 216 entries.  Then you have the exact probability of your Gurps table. From the Interent, Someone Smarter than I Roll Probability Gurps Probability Probability of a sum of 3: 1/216 = 0.5% 3 1 3-4 4 Probability of a sum of 4: 3/216 = 1.4% 4 3 5 6 Probability of a sum of 5: 6/216 = 2.8% 5 6 6-7 25 Probability of a sum of 6: 10/216 = 4.6% 6 10 8 21 Probability of a sum of 7: 15/216 = 7.0% 7 15 9-10 52 Probability of a sum of 8: 21/216 = 9.7% 8 21 11 27 Probability of a sum of 9: 25/216 = 11.6% 9 25 12 25 Probability of a sum of 10: 27/216 = 12.5% 10 27 13-14 36 Probability of a sum of 11: 27/216 = 12.5% 11 27 15 10 Probability of a sum of 12: 25/216 = 11.6% 12 25 16 6 Probability of a sum of 13: 21/216 = 9.7% 13 21 17-18 4 Probability of a sum of 14: 15/216 = 7.0% 14 15 Probability of a sum of 15: 10/216 = 4.6% 15 10 Probability of a sum of 16: 6/216 = 2.8% 16 6 Probability of a sum of 17: 3/216 = 1.4% 17 3 Probability of a sum of 18: 1/216 = 0.5% 18 1

Thanks I appreciate the help!! So can the percentages in a Rollable Tables be decimals (0.5 or 2.4) or is that where you are talking about rounding?

From reading above I think you can use weighting to make the entry much easier. Just weight each entry as per the table I had shown.  Its like you are rolling a d216.  1-4 you get the first entry, 5-10 you get the 2nd entry, etc. Gurps Probability Percentage 3-4 4 1.851851852 5 6 2.777777778 6-7 25 11.57407407 8 21 9.722222222 9-10 52 24.07407407 11 27 12.5 12 25 11.57407407 13-14 36 16.66666667 15 10 4.62962963 16 6 2.777777778 17-18 4 1.851851852 Total 216 100

GManator said: Thanks I appreciate the help!! So can the percentages in a Rollable Tables be decimals (0.5 or 2.4) or that were you are talking about rounding? Don't use percentages.  Just create a table with 11 entries just like your gurps table.  Then in the weighting option just type the numbers I put in above and it will be perfectly weighted.  (I think) :)

Edit - Ignore me here.  Easier (and correct) way below. Konrad J. said: A few people beat me to it, but I think this may be a better solution than percentage since there is no rounding. So you need a table with 216 entries.   Yeah, there's a cost benefit analysis to be done here.  You can make an 11 entry table and deal with some rounding, or you can make a 216 entry table and have it be "pure."  In the end, I felt it was just easiest to do a 3d6 roll and look it up on my cheat sheet, YMMV.

Edit - I am wrong in my interpretation here. &nbsp;Closer reading would have worked better for me. &nbsp;Either a percentage adding up to 100 or a total weight as Konrad indicates works. I believe the weighting needs to be in a percentage of 100 - check the docs. &nbsp;You have to do the rounding, or else make each entry. You can additionally add "weight" to items in two methods; either enter the number of times you want the item be a possible result OR enter a percentage value. When using percentage values, do not place "%" after the number, and the final number of all items that are elements of the table must equal 100. <a href="https://wiki.roll20.net/Card_Decks_and_Rollable_Tables" rel="nofollow">https://wiki.roll20.net/Card_Decks_and_Rollable_Tables</a>

Dave D. said: I believe the weighting needs to be in a percentage of 100 - check the docs. I might be wrong, but I think Riley is simply telling you that if you want it entered in % then the total needs to be 100. &nbsp;But I might be wrong since I've never used the rollable tables myself. &nbsp;I'm assuming if the number of weighting adds to 100 its percentage, basically a d100. &nbsp;If it adds to some other number then its "d" something else. &nbsp;If its not like that then it might be good to change it to be like that. &nbsp;THen its easy to create rollable tables like this. You can additionally add "weight" to items in two methods; either enter the number of times you want the item be a possible result OR enter a percentage value. When using percentage values, do not place "%" after the number, and the final number of all items that are elements of the table must equal 100.

If you enter a decimal in the "weight" field, it truncates down to an integer. Let me field test this out real quick...I wonder what happens if you put a weight of 216 in.

Well, I think I'm going to stand corrected here. So, if you make a rollable table using a weight that adds up to 216, it doesn't kick an error and you get results that are to be expected. &nbsp;I got a "Body" result 12 times out of 30 (which is reasonable). &nbsp;Awesome! This makes the table really easy to use now...just put a weight equal to Konrad's probability field in his post above... Skull would get a weight of 4, Face would get a weight of 6 and so on.

Dave D. said: Well, I think I'm going to stand corrected here. So, if you make a rollable table using a weight that adds up to 216, it doesn't kick an error and you get results that are to be expected. &nbsp;I got a "Body" result 12 times out of 30 (which is reasonable). &nbsp;Awesome! This makes the table really easy to use now...just put a weight equal to Konrad's probability field in his post above... Skull would get a weight of 4, Face would get a weight of 6 and so on. Ah good to hear. &nbsp;I created a thread in the Mentor forum stating if it behaves the way I thought that the Wiki entry might want to be changed a bit. &nbsp;Its a bit confusing perhaps, but I think Riley was just trying to give an example of how to create % dice.

Yeah, to make matters worse I was going on how this worked at first. &nbsp;Which made it near useless. &nbsp;This rocks now. Thanks Konrad!

Dave D. said: Yeah, to make matters worse I was going on how this worked at first. &nbsp;Which made it near useless. &nbsp;This rocks now. Thanks Konrad! I found something strange. &nbsp;I created the table and named each entry &nbsp;after the number range just for test. So 3-4, 17-18, etc. &nbsp;I then noticed it would tell you what it rolled and then also put down = and then the first number in the name of that entry. &nbsp;So it would roll and then come back with (17-18) = 17. &nbsp;I change d the entry names to letters and I get (a) = 0. &nbsp;Here is a screen shot. &nbsp;I guess the number result is so you can create custom sized dice and have an integer result? &nbsp;It takes the numbers in the entry name up until any non numbers I guess.

Thanks for this guys. I gave you props in the GURPS 4e section of the Roll20 wiki!!