Hi all and merry Christmas!

Casual player here, wanting to improve. Just purchased XG!

If it's okay then I'll keep posting in this thread instead of starting new ones each time?

I would naturally have done 13/7 (2) for this roll. Maybe even 13/4, 4/1 as you should always aggressively hit blots right?

XG says it's more important to hold the 5 point instead of holding the 6, 7 and 8 point. Is this usually the case? I should be aiming to hold the 5 point as opposed to a strong builder (I forget the correct terminology) to more easily block their pieces in my home board?

Next question already..!

Is there an obvious answer why 24/23 13/7 is so much worse than 23/22 13/7?

Thank you

Sorry for all the questions. Here's the next situation in same game as above:

Given the learning experience from my first post above, I thought that after Bar/22, 21/18, the next move would be 8/5 (2). But apparently not - XG says it should be 13/10 (2). But surely we want to protect the 5 point here, given the opponent has 2 pieces coming in from the bar and could then get an anchor on the 5 point?

Answer to #2:

Advanced anchors are very valuable. But anchors on the 1- or 2-point are usually problematic. Instead of making such a bad anchor it's usually better to distrbute your checkers on different points to have more flexibility in the future. (But there are exceptions: In a blitz you take every anchor you can get.)

Answer to #3:

Your move makes a hole into your 4-prime. The 8-point will be a good opportunity for your opponent to escape. XG's move improves the 4-prime to a 5-prime which is incredibly valuable because the opponent has to be very lucky to come over a 5-prime.

Thanks for the replies cornelius. XG is showing me how much of a beginner I really am..

Your answer to #2 makes complete sense.

If we apply your answer to #3 back to #1, 13/7 (2) would have created a 3-prime and giving me a nice position to build on...struggling to get my head around why taking the 5 point is more advantageous than a 3-prime in that situation, but in #3, it's more advantageous to leave the 5 point and build on the prime.

Is it simply because a 5 prime is considered so strong and a 3 prime isn't really, therefore forget about the 3 prime and just take the 5 point?

Hopefully that all makes sense.

Another one now

Why is XG telling me to take a double when it says I have a 29.39% chance of winning? Maybe because I have it set to the "unlimited games" option?

Nope, in the next game which is now a match up to 9. It wants me to take another double when I've got a 31% chance of winning

With primes it is the same as with anchors: The higher ones are extremely valuable whereas the lower ones are worth nothing at all.

A very basic rule of thumb is that you should take above 25% winning chance. (But there are of course many exceptions. Gammon threat or score can complicate this.)

Thanks - all understood.

I found a website which talks about the doubling cube and 25% figure - https://bkgm.com/articles/Youngerman...eStrategy.html

"Should your opponent take? This is easy. He should take when he is 25% or more likely to win the game. Say you have 4 games where your opponent doubles when you are 25% to win. If you drop all four, you'll lose four points. If you take all four and win one, losing three, you'll break even compared to dropping all four - losing four points. "

If you take 4 doubles, and win 1, then you lose 8 points but win 2 points...so you're 6 points down?

I would explain this differently:

Let's say your probability to win is 0.26 and the probability to lose is 0.74. Why should you take?

If you drop your result is -1.
If you take the expected value is 0.26*2+0.74*(-2)=-0.96
Therefore taking is slightly better.

When you make the same calculation with 0.25 you will see that the results are equal.
When you make the same calculation with 0.24 you will see that dropping is better.

Thanks cornelius, but it's been a little while since I did maths in school Please can you breakdown that formula?

I was following the explanation on that website, until it said -8 + 2 = 0!

If you take 4 doubles and win 1 of those, that means you lose 3 games. So you lose 6 points in those 3 games and win 2 in the 1 game you win -- you're 4 points down, same as if you dropped all 4 cubes.

Thanks Z

You're completely right...I was being a bit thick. So it would be -6 + 2 = -4, which is the same as passing on all 4 games.

So the theory is that if your odds are over 25%, then the odds are that you win around 1 in 4, but you might win more than 1, in which case you're up so you might as well take all 4 doubles?

Without a program like XG, how are we supposed to tell our (rough) odds?

Hope you don't mind if I also ask a couple more questions about XG - in the screenshot below:

1. Why are there two difference percentages? (to win the game?)
2. Why aren't the best moves shown in order (highest to lowest percentage)?
3. What's the difference between moves shown in black vs moves shown in green?



Thanks all

Why would XG tell me to play a move that has a lower percentage of winning the game than the move I chose?

The move I chose had a 18.59% chance of winning, but the move at the top of the list (which XG gives me a hint to take) is 17.78%.

Oh I think the two different percentages (post #13 question 1) are game winning percentage and match winning percentage.

The idea is to show that if you win over 25%, you are better off taking, if you are below that you are better off passing, and if you are exactly that, then it doesn't matter what you do.

But really that 25% number is just a starting point/oversimplification. Your take point is rarely exactly 25% due to three factors that can push it up or down:

1. Gammons/backgammons
2. Match score affects when you should take or pass
3. When you take, you have sole cube access, which is an advantage, so can typically take a little deeper than the simple math indicates

Thanks Z, all makes sense. How do you tell your rough % with a program?

I mean without a program..!

Generally people don’t try to estimate percentages over the board, they just get familiar with what doubles and takes and passes look like for various position types (blitzes, holding games, etc.) in a money game or at 0-0 in a long match, and then go from there.

Thank you. Any insight you could offer to the XG questions above would be appreciated!

Referring to the last problem (White to play 6-4) you've overlooked that you get gammoned more often with your play. Since you're leading 3-1 to 7, that's a big deal.

Hi Robertie! Thanks for the reply.

I think I see that now, I wasn't looking at those figures before.

The move I chose results in a 25.41% of me being gammoned, whereas the move suggested by XG has a 20.57% chance of me being gammoned..

That's why the best move for the game might not be the best move for the match! Understood now, thank you.

I don't suppose you're able to explain why 12/8 12/6 has less of a chance of being gammoned than 13/3? Is it just because I'm getting 2 pieces into my home board instead of 1?

I’ll take a crack at this (but will obviously defer to Mr Robertie if he disagrees):

Having a second checker hit at this point would greatly increase your chances of losing gammon. Your opponent is in great position to attack and close out your straggler; adding a second blot makes it likely he’ll close out two checkers, which would obviously lead to a lot of gammons. You need to play as safely as possible so as not to expose a second blot.

The problem you have before this roll is that your position is fairly stripped and inflexible. You have the spares on the 13 to play with, but that’s it. You can use them for another roll or two, then you’ll be forced to break a point, and unless you get a lucky roll you likely will expose a blot. Playing 13-3 just eliminates another spare, putting the inevitable breaking of a point closer. 12/8 12/6 effectively creates two new spare checkers to play with, giving you a more flexible, and therefore safer, position.

Thanks for your explanation Stremba.

Just to clarify this bit - "Your opponent is in great position to attack and close out your straggler; adding a second blot makes it likely he’ll close out two checkers, which would obviously lead to a lot of gammons. You need to play as safely as possible so as not to expose a second blot."

Are you talking about the following?

13/3 leaves a blot in my home board
Opponent attacks blot on ace point
I roll a 14, 15, 16 and take opponent's blot on ace point
Opponent rolls a 3
Opponent takes my blot on 3 and then I have 2 pieces in opponent's home board

Thanks

While what you described may happen (especially since your opponent should be hitting loose and slotting the front point of his prime), it’s not exactly what I had in mind. You need to consider how the next few rolls are likely to play out.

Look at your position before moving that 64. You have only two checkers you can move (not counting your trapped back checker - you’d have to try running it out if you get the opportunity) without breaking the 13, 12, 8 or 6 point. When you break one of these points you are likely to leave a blot unless you get a lucky roll. If you can wait a few more rolls, your opponent may be forced to move his back checkers homeward and leaving that blot wouldn’t be so dangerous.

After 13/3 you now only have one checker to move without breaking a point — the third checker on the 13. With 12/6 12/8 you create two new spare checkers, the third ones on the 8 and 6 points plus the two spares on the 13, for a total of four spares rather than one. You are far more likely to be able to play safely until your opponent is forced to break contact.