Don't sell on bad news.
Before selling, try to re-evaluate the company again and see where the stock sells in realtion to its book value.
Don't be afraid to be a loner but be sure that you are correct in your judgement.
You never get the high and you never get the low.
My first job at Graham-Newman was to prepare the annual report for that 10th year.
I agree with Warren to keep it simple and not use higher mathematics in your analysis.