how to chart for multiple data?

[zimorok]

`#!/usr/bin/env python3
from pyspc import *

a = spc(pistonrings_a) + cusum() + ewma() + rules()
b = spc(pistonrings_b) + cusum() + ewma() + rules()

print(a)
print(b)

from the example above, how to show all the graph in the same window?
If I run the code above, only a will be shown