stop loss for investors ,easy calcualtion

I have seen many web pages and other references on this subject . Practically all of them are only for TRADERS, who play for short time(one day to 5 days). Those calcualtions are complex. There appears to be no objective method of calculation of stop loss for medium(3 to 12 months) and long term investors. The only advice given is a vague answers talking about risk profile etc. Risk profile cannot be so divergent.Even if you are millionaire you would not like to take a risk of 80% suppose I am prepared to keep an equity for 3 years. but what stage of loss should I get out. Is there any tolerably specific answer. sometimes you buy a scrip for Rs 200. assuming fundamentally it was a good stock and like to keep for three years, but it goes down and down to 20 rupees. at what stage should I accept the loss and get out. somebody should think on these lien and give a fairly objective method of calculation of stop loss for such investors. Many may not have time and facility to do some complex calculation. Those who have rich experience of INVESTING in equities should give us an answer. At least they can tell us what is their tactics.