'Return the unit value and the default units specified
from the given keyword arguments dictionary.'

def default_units(self, kwargs):

    val = 0.0
    default_unit = self.STANDARD_UNIT
    for (unit, value) in kwargs.items():
        if (not isinstance(value, float)):
            value = float(value)
        if (unit in self.UNITS):
            val += (self.UNITS[unit] * value)
            default_unit = unit
        elif (unit in self.ALIAS):
            u = self.ALIAS[unit]
            val += (self.UNITS[u] * value)
            default_unit = u
        else:
            lower = unit.lower()
            if (lower in self.UNITS):
                val += (self.UNITS[lower] * value)
                default_unit = lower
            elif (lower in self.LALIAS):
                u = self.LALIAS[lower]
                val += (self.UNITS[u] * value)
                default_unit = u
            else:
                raise AttributeError(('Unknown    unit    type:    %s' % unit))
    return (val, default_unit)
