8042.....The way I made money on my ISYS holding...buying in at 10p.....was to Sell part of my holding on the way up.....So in your position what I would do is as follows.....You have 500.000 @ 17p....
19p....Sell 100.000.....£2.000 profit. (If it reaches 19p then drops to 18p rebuy).
21p....Sell 100.000.....£4.000 profit (if it reaches 21p then drops to 20p rebuy)
23p....Sell 100.000.....£6.000 profit (if it reaches 23p then drops to 22p rebuy)
25p....Sell 100.000.....£8.000 profit (if it reaches 25p then drops to 24p rebuy)
27p....Sell 100.000.....£10.000 profit (if it reaches 27p then drops to 26p rebuy)
If the price doesn't drop then you make £30.000......I know that if you hadn't sold on the way up you would have made £50.000.....but shares rarely go up in straight lines.....I made over £100.000 on ISYS using this method...