Expected behavior of the Back button in a non sequential process?

Question

I'm working on an app that lets the user combine different options to build a product. The process is as follows:

Screen 1. A first screen where the user decides what to build.

Screen 2. Second screen where the user sees all Options as tabs. The user can switch between tabs to play with the options and do some selections in each tab, in any desired order. This 4 selections happen in the "same canvas".

*Tabs do not follow a strict order, so there is no sequential steps involved (no previous or next buttons within Screen 2)

The question is: Will a user expect the BACK button to take them to the Screen 1, OR to the previously selected tab within the Screen 2?

Here's a quick sketch of Screen 2:

Any advice is much appreciated. Thanks!

Answer 1

DA01 makes a great point that testing will probably get you farther than asking the internet, but I suspect that you'll get a variety of expectations as it's ambiguous in its current state. However, you can control the user's expectations by labeling your button more descriptively. taswyn gives a great example in an answer to another question regarding back buttons:

For example, consider whether someone would have any uncertainty over what the following might do:

• Back (Back to where? also applies to the browser's back button, because we all know it doesn't always do what we expect, depending on the web app, and people don't know what your app will do until they try, which can be a hesitation point)

• Back to listings (which listings? if I come here from a bookmark, do I have any clue what I was doing that got me here?)

• Back to [associated product category] (Well, that's nice, it is functional and not a concern for failing to be deterministic, but should probably be represented elsewhere)

• Back to the January Sale Event (hey! that's what I was looking at when I came here! it's specific enough that I can expect to end up… where I would expect to go) (aka it matches the navigation context map that brought me to this page)

I understand that space may be at a premium if you're working on mobile, but having the button read Start Over would clearly indicate the button would take the user back to Screen 1, while naming it Previous Option would clearly stay on Screen 2 and go to the previous tab. If you expect users to desire to do both and you can afford the real estate, you could add a second button and allow users to use either.