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Thread: True count calculation: the effects of rounding

  1. #1


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    True count calculation: the effects of rounding

    I've been using the Blackjack Apprenticeship training app, and I've noticed that they round in two different ways that compound error in true count calculation: decks remaining shows as 'n' until it drops below 'n - 1' (e.g. 3.1 shows as 4 -- not only does it show as 4, but 4 is what gets used in the subsequent TC calc), and the true count is always rounded down to the whole number. Both of these effects work in the same direction -- they artificially lower the true count. I had a running count of 7, actual decks remaining of just over 3 and therefore reported as 4, which spit out a true count of 1! (1.75 rounded down / truncated to the whole number.) The actual TC in this case is above 2. By their own deviations chart (total of 26), a few of those are triggered at 2. If the same rounding inaccuracies yielded TC of 4 when it was actually 5, no fewer than 5 deviations would be missed. That doesn't seem acceptable when those 5 are of the most important 26 deviations out of more than 100.

    My question is this: does anyone know whether their deviation indices take any of these rounding inaccuracies into account in such a way that would minimize their bad effect? Or do they just round the simulation trigger index to the nearest whole number? E.g. if they are recommending or assuming that their followers will use a 'whole number & round down (rather than to the nearest)' approach, which tends to underestimate the true count, dramatically so as DR gets small, do they get some of this back by also rounding the simulation trigger index? E.g. if the simulation says you should start splitting your 10s against dealer 5 at TC of 5.9, and knowing that people might have an actual TC close to 5.9 when their crude estimation is coming out closer to 5, might they report this on the chart as index 5 rather than 6?

    I'm asking because I like their chart and the idea of a 'Top 26' deviations, at least to start, but I don't want to use a chart which has 'corrections' to a crude rounding system that I won't be using. Then the corrections themselves introduce large errors for people using a more precise TC calc. I will be using decks remaining increments of closer to 0.25, especially when DR gets low, and rounding TC by no more than 0.5.

  2. #2


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    CountDrewcula,

    The correct way to calculate remaining decks and to resolve fractional TC's is to use the methods that were used to generate the indexes you plan to use. Thus, if the indexes shown on the BJA chart were generated by "ceiling" (as opposed to flooring) the decks remaining and "flooring" the fractional TC's, then those are the correct methods to use.

    If you want to use different methods, then you should generate the indexes using those methods. Norm's outstanding CVData can handle almost any combination of deck estimation method and fractional TC resolution, including the ones you mentioned.

    Hope this helps!

    Dog Hand

    P.S. Kudos to BJA for explaining their methods to the level of detail you indicate. Sadly, most authors leave their readers in the dark about such minutiae.

  3. #3


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    I would add an important comment. BJA can enunciate any method they choose to estimate decks remaining and ultimately convert RC to TC. But I'm not altogether certain that they then use that precise method to generate their own indices, as opposed to just using widely published indices for, say, Hi-Lo. So, as the OP indicates, if there is a mismatch between the way BJA calculates TC and then subsequently uses that value to create indices (or not!), then that could be a definite problem.

    Don

  4. #4


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    Don,

    Thank you. I will try to get a response from them. Take care.

  5. #5
    Senior Member BetWise21's Avatar
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    I'm a hi-lo counter that floors the TC conversion. I think the best resource for floored indexes is the first edition of Professional Blackjack by Stanford Wong and I also use and compare that with Ken Smith strategy cards. I would like to know if anyone has other suggestions to choose indexes. I have CV data and have made some attempts to generate my own set of indexes but am not confident that I am making the right choices when running the Sims.
    "between the conception and the reality, falls the shadow "

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    The Hollow Men

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