def tick_value(decimals=1, unit=''):
    """A tick formatter to display the y-axis as a float value with a given unit symbol.

    Args:
        decimals = 1: The number of decimals to display.
        unit = "": The unit symbol to concatenate to the value.

    Returns:
        A tick formatter function (f(y, position)) displaying y as a float with a unit symbol.

    """
    return lambda y, position: '{:+,.{decimals}f} {unit}'.format(1.0 * y,
        unit=unit, decimals=decimals)
