CATEGORY:
    Knuth: Blunder (Thinking the right thing but doing it wrong)
    
REFERENCE: 
    https://www.tug.org/TUGboat/tb10-4/tb26knut.pdf

EXPLANATION:
    The following code ensures that four double-strikes are done whenever the
    current hour is evenly divisible by four:
    # Correction for four double-strikes at 00:00, 04:00, 08:00 ...
    if double_strikes == 0:
        double_strikes = ShipBell.MAX_DOUBLE_STRIKES
    However, this condition is also true for all minutes following that hour,
    which is not what is desired.

CONSEQUENCES:
    Whenever 'double_strikes' is 0, 'double_strikes' is unconditionally set to
    'ShipBell.MAX_DOUBLE_STRIKES', even half an hour later, when
    'single_strikes' has changed to 1. Consequently, the bell pattern is "2 2 2
    2 1", when it should be "1".

BUGFIX:
    The correction for four double-strikes shall only be done exactly on the
    hour, when 'minutes' equals 0:
    # Correction for four double-strikes at 00:00, 04:00, 08:00 ...
    if double_strikes == 0 and minutes == 0:
        double_strikes = ShipBell.MAX_DOUBLE_STRIKES

REMARKS:
    The full code of the Ship's Bell app can be found here:
    https://github.com/ralfholly/ships-bell