A static approach to mobile reading.
Come to think of it this is how you read posts on Bulletin boards but that’s a long time ago so I might be wrong, a long long time ago 
Man those were the days!
Ok, I thought in the absence of visual mock-up. Let me use the topic progress widget analogously.
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Widget open = Imagine full screen post view
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Time line up or Down = pgUP / pgDN
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Post preview = Full post (displaying section of, if larger than available screen)
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Transition none = Transition none.
For example, Tapping down moves you through the content incrementally, one tap at a time - which more accurately describes the idea as opposed to my earlier comment “one post at a time”.