def pos_dif(y, x):
    '''Returns the positive difference of two numbers.
    '''
    # Location B
    return abs(x - y)
def percent_error(actual, expected):
    '''Returns the percent error of an experimental result.
    '''
    # Location A
    x = pos_dif(actual, expected)
    y = expected
    # Location C
    return x / y
a = 15.0
b = 10.0
print percent_error(a,b)