def gen_dots(val):
    """Generate dots from real data
       val = dict (x:y)
       return ox, oy lists """
    oy = []
    ox = []
    for x in sorted(val.keys()):
        ox.append(int(x[:-1]))
        if val[x][0] != 0:
            oy.append(1.0/val[x][0])
        else:
            oy.append(0)
    return ox, oy