0040h:0070h           Timer Overflow flag

    Length: 1 byte

    Keeps track of whether midnight has passed since the machine was
    powered on. See the 4-byte integer counter at 0040h:006Ch for more
    details.

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    Note that this byte is only a flag. It either has a value of 0 or
    1. Therefore, it won't reflect a day change over a two-day period.

    Use Int 1Ah, Service 00h, to obtain this overflow value. Note that
    doing so clears this byte.