I'm attempting to do my own math for some plays, and I've run into two versions of DI.

In my copy of Blackjack Attack (3rd edition), p.203:"I have christened this ratio the "Desirability Index" (DI) and have defined it, for any game, to be equal to one thousand times (for convenience of expression) the ratio of that game's per-hand-seen win rate to the per-hand-seen standard deviation."

In other words, DI = 1000*EV/SD.

However, here (https://www.888casino.com/blog/side-bets/fear-loathing-and-blackjack-side-bets), Eliot claims to quote from BJA as well, but makes an exception for back-counting plays.

I have christened this ratio the “Desirability Index” (DI) and have defined it, for the play all game, to be equal to one thousand times (for convenience of expression) the ratio of that game’s per-hand win rate to the per-hand standard deviation.Is there any reason it's reduced by a factor of ten for backcounting games? Is this simply out of date information?Similarly, for the back-counted game, DI = 100 times the ratio of that game’s win rate per 100 hands to the s.d. per 100.

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