def tick_maker(old_ticks,n):
    """Set n-1 evenly spaced tick marks to make axes look prettier"""

    if n < 2:
        raise ValueError('n must be greater than 1')

    n = n-1
    delta = (old_ticks[-1] - old_ticks[0])/n
    new_ticks = []
    for i in range(n):
        new_ticks.append(old_ticks[0] + i*delta)

    new_ticks.append(old_ticks[0] + n*delta)
    return new_ticks