Difficulty levels

[steve...@googlemail.com]

I think your app is superb , I've been playing for years!
Call me an idiot , but I've never been able to work out the difficulty levels ? Which are easy and which are difficult etc . I dont know what ply means ...
It all seems pretty hard to me ...and I am an above average player !

[ibti...@gmail.com]

so as per i know ply in chess is a half-move.  
In computing, the concept of ply corresponds to one level of the game tree. its actually the layer that computer would typically search to a depth of between a range say 1-10 (as in the application). so 10 ply is the hardest and 1 ply is the easiest level. 
I hope that helps.