Well, it’s a mystery to me anyway.
I am building a Adirondack chair. The plan I am using has a very specific asymetrical shape to the seat back.
Is this just some random designer’s whim, or a specifc shape from a specific period?
Here is the shape:
Do you know what the design is called?
Never seen one that shape before, so I’m going to guess “random designer’s whim.” Or perhaps “designer’s random whim.”
All the chairs of that design cranked out by our school woodshop are symetrical. I’d say the designer of that particular chair is just messing with you.
I think that designer must’ve been afflicted with some weird condition where his right shoulder is hitched up several inches above his left. I’d mirror image the back of that chair-- either side, whichever way you like it. I’ve never seen anything like that. In fact, it makes me feel uncomfortable just looking at it.
It looks kinda like parts from two similar but not trulymatching chairs.
Like building a car from Chevy Camaro AND Pontiac Firebird parts: It’ll fit together and work, but it looks funny.
I say it’s a mistake. If a designer wanted an asymmetrical design, he wouldn’t have just changed that one piece. the entire back would be different. I’d go with asymmetry only if I were making two chairs, and they mirrored each other.
Pick the side you like and change the other side.
Perhaps the idea was to give 2 options in one plan.
Perhaps this was the idea.
Maybe it was designed like that so you can sort of sit a little sideways, so if you were talking to someone sitting in the chair next to you it would still provide nice support.
Thanks for your replies.
I will make two - a left and right version as suggested. My wife agrees that it looks odd on the plan, but I cut out the pieces for the backs and it looks ok in an actual example.
From an online chair manufacturing site, I found the reason that the Adirondack chairs are so low to the ground and difficult to get out of (fall out of?) is because they were designed to be used on hilly terrain.
But as pointed out, there are no examples of an asymetric back shape in photos. It’s tempting to do it just to annoy people. 
Could I call the back shape art deco or art nouveau and get away with it? It looks a bit like a stylised duck or bird tail.
that does seem likely. Perhaps it is so your woman servant could serve you drinks from the left or right hand side more easily.
If that’s the case, you have to shorten two of the legs (and invite PDQ Bach over). 