I am still in need of this if anyone knows of such an app. I did get in touch with the designer for "Analyze This" a couple weeks ago and he said his team is working on a fix, but no updates since then.
Iphone Analysis App that can be held horizontally?
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I just wanted to let people know that the designer of "Analyze This" and his team released an update today that should fix the issues I was complaining about. He has been very responsive by email and I am looking forward to testing the update and studying my butt off with this app! Interacting with him by email has been a very refreshing experience. I have gotten used to too many companies taking ages to resolve similar issues or being outright indifferent to such problems. So it is wonderful to see these guys working so hard to improve their very underrated app that likely doesn't generate much income. I always try (and often fail) to be a "principles over money" kind of guy myself, so guys like this certainly give me hope.
I highly recommend giving the free version of this app a try. It allows me to hold my chess book in one hand and my phone in the other while I play through games and variations. This is far more efficient for me than using a real board (very time-consuming to play through variations) or a desktop/laptop (very awkward and a bit slower). Additionally, I can quickly play through lines not mentioned in the books I am studying and get the answers to my questions from the embedded Stockfish engine. And I can do all of this while lying down which gives my not-so-good back a much needed break! It is also great for sharing my latest games with friends.
There are obviously other similar apps, but the ability to hold the app horizontally makes it possible for me to do everything with one hand and hold the book with the other. I cannot do this with a vertically held analysis app on my iphone, as everything just becomes too small. Highly recommended! 
I use an app called "Analyze This" for my iphone. It is the only analysis app that I have found that runs stockfish and can be held horizontally. Every other app I have tried only allows me to hold my iphone vertically. The problem with "Analyze This" is that it is buggy and often crashes 1-2 times by the time I finish going through a GM game. I have emailed the designer for assistance, but do not have my hopes up and need a new option until he fixes the bugs. I do love the features and design other than the bugs though!
I do most of my study with my iphone in one hand analyzing and my chess book in the other. I find that this is far more efficient than using a real board. Playing through variations and returning to the main line is much faster this way, for example. And when I reach spots where I don't understand a situation and the annotations aren't helping, I can turn on the engine and be like "Oh ya! Moving my knight would allow so-and-so tactic..."
Thank you for any app recommendations!