def bpm2bcl(bpm, m=0.001):
    """
    Converts a beats-per-minute number to a basic cycle length in ms. For
    example a bpm of 60 equals a bcl of 1000ms.

    >>> import myokit
    >>> print(myokit.pacing.bpm2bcl(60))
    1000.0

    To use a different unit scaling, change the optional parameter ``m``. For
    example, with m set to 1 the returned units are seconds:

    >>> print(myokit.pacing.bpm2bcl(120, 1))
    0.5
    """
    return 60.0 / m / bpm
