This is sometimes called the Fabacci method .(famous Italian mathamatician)
The idea is to add both ends together as indicated , but the amount crossed off should be related to the odds .
E.g. odds 1/1 cross off one number from each end ( as mentioned by Crash)
2/1 cross off 2 numbers from each end.
5/1 cross off 5 numbers from each end.ect
Before adding the 2 ends again.

It can work, so as long ones run of outs is not too sevear.
One needs a cut off point where one says enough is enough .
Then start again.

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Cheers.