Do all the grandma double CPS upgrades stack on each other or do they only affect the first upgrade that gives +0.3 CPS.
For example if all the double upgrades stacked grandma's CPS would be:
upgrade 1: 0.8CPS
upgrade 2: 1.6 CPS
upgrade 3: 3.2 CPS
upgrade 4: 6.4 CPS
etc.
but if they only stacked with the first upgrade:
upgrade 1: 0.8 CPS
upgrade 2: 1.6 CPS
upgrade 3: 2.8 CPS
upgrade 4: 5.2 CPS
upgrade 5: 10 CPS
etc.