Falling down water?

I had planned something altogether different, but they've been juggling again.
The Plan:-
In the cereal aisle: one side was labelled "Adult cereals"; across the way there was a label reading, would you believe, "Healthy cereals".
Make of THAT what you will.
One of the signs has gone went; next project - read sugar content of "Healthy cereals".
On my way to the tills, what better aisle to toddle through than the beers?
Being partial to the odd Guinness, or 4, on alternate Wednesnights and ever the sucker for the odd/different, I spotted this line-up.
From the left:-
"Original" -  -  -  -  500mls - 4.2% - 2.1 units.
"Porter"  -  -  -  -   500ml - 6.0% - 3.0 units.
"Foreign extra" - 330ml - 7.5% - 2.5 units. Falling down water, offset by reducing the volume. Considerate of them?
Having supped, and noticed the hue of #3, similar to that we are accustomed to, I decided to look up "Porter"; never having been sure of the difference.
"Let’s just say this right off the bat: trying to understand the difference between a porter and a stout in today’s craft beer world can be a pretty dizzying experience. That’s because over the past ten years or so, in many craft circles, the names have been used pretty interchangeably when categorizing darker beers."

Found here, if you'd like to know in depth.
;¬)