def METHOD_NAME(self, val_ms):
    '''return a speed as a string'''
    if self.settings.speed_unit == 'knots':
        return "%ukn" % (val_ms * 1.94384)
    elif self.settings.speed_unit == 'mph':
        return "%umph" % (val_ms * 2.23694)
    return "%um/s" % val_ms