Forgive me if this has been raised before, but I'd dearly like to know if anyone knows of any good books/techniques/training programs for improving one's ability to calculate/visualise. I'm also interested to know of anyone who has used such techniques and whether they have noticed any improvement.

In particular, what does one do about the following: after calculating more or less accurately for a certain number of moves, one gets to a point where the resulting position is vague in one's head, and one loses the confidence or ability to proceed. How do you clarify the mental picture (assuming, contra Wittgenstein, that it is ultimately a matter of visual imagination) and extend the range of calculation?

Thanks in advance for any help

Cheers - PaulB