Prime against prime games require finely honed judgement and are amongst the most difficult of all game types to play. In a blitz, once you have embarked upon it, most of the moves are clear, in a prime vs prime each individual move will require much more thought.

In particular, the use of the doubling cube is of paramount importance, and it is here that a good player will really show his understanding of the dynamics of the game. Prime vs prime games often end in a gammon for one side or the other.

The diagram shows the typical late stages of a prime vs prime: Black is on roll.

Both sides have five point primes (five consecutive points) and have two clear objectives, firstly to extend the prime to a full prime (six points) and secondly to escape the checkers that they have trapped behind their opponent's prime. For example, if Black were to roll 6-2 in the above position his best move is to play 23/17; 4/2*. He could make a full prime by 8/2*; 4/2 but that prime would immediately be broken next roll unless he rolled another 6.

Doubling requires fine judgement not only of the position but also the ability to estimate your opponent's evaluation of his chances. In the above position Black has a slight advantage based on the fact that he is on roll in a very volatile position and he has slightly better timing (more on the concept of timing in future articles but here it means that Black, if he does not roll a 6, will keep his prime for longer than White). Black should not double, and White if doubled should take. However, I had this position as Black in a recent game and I knew that White would probably mis-evaluate the position. I therefore took the risk of giving an unsound double. Imagine my pleasure when White dropped in a matter of seconds - a huge and costly error, proving once again that the most expensive mistakes in backgammon are nearly always made with the doubling cube.