def to_metric(amount, unit):
    """
    Used to convert common (amount, unit) pairs to metric versions, e.g.,
    (5, 'GALLON') -> (18.9270589, 'LITER')
    """
    if unit == 'POUND':
        kgs = (amount * 0.45359237, 'KILOGRAM')
        if kgs[0] < 1.0:
            return (kgs[0] * 1000, 'GRAM')
        return kgs
    if unit == 'OUNCE':
        return (amount * 28.3495231, 'GRAM')
    if unit == 'GALLON':
        return (amount * 3.78541178, 'LITER')
    if unit == 'TEASPOON':
        return (amount * 0.00492892159, 'LITER')
    if unit == 'TABLESPOON':
        return (amount * 0.0147867648, 'LITER')
    return (amount, unit)