You can do this with Stockfish. When the evaluation of the engine changes dramatically, it just means you probably did something really horrible.
It won't improve your chess, by the way, if you just let the engine do everything for you. You should take a look at the game yourself first, think carefully, and then check your ideas with the engine.
Thanks for the response but I need an idiot's guide - an indicator if the assessment changes drastically. I take your point about checking the games manually though.
The indicator is the engine evaluation. If you go from +0.3 to -2.4 or something, that means you did something very wrong.
Can anyone point me in the right direction? I currently use Stockfish on my I-pad but I want an Engine that will show me when I made a make a blunder, mistake or inaccuracy. Something which relicates the Chess analysis feature would be perfect. I am not interesting is the evaluation after x moves, merely a flag to show which move was the mistake.