Well, think of as an insurance policy (rather than a stop-loss perhaps) on which you expect to pay a premium. Sometimes, though, it'll surprise you and it'll pay you!
In your example if FTSE went up 20 and DOW went up 20 then you'd make a bit : £10 x 20 for FTSE = £200, £5 x -20 for DOW = - £100. That'd be FTSE trading strong.
Conversely if FTSE went up 10 but DOW went up 30 then you'd lose a bit : £10 x 10 for FTSE = £100, £5 x -30 for DOW = - £150. That'd be FTSE trading weak.
Remember why I started this!! You were long FTSE and thought it could fall back quite a bit and still have the up-trend intact. The price did fall back and you were a tad concerned that the pull back might be extensive and/or turn into a reversal. Thus, you set a stop below the current price which took you out and you counted your profit.
I suggested that you hedge it instead and showed that you'd have made a bit more money closing both trades at FTSE close despite FTSE having dropped. You could, of course have lost a little had FTSE traded weak from when you hedged. Let's say you decided to keep the trades going because you still felt FTSE was in up-trend. As of now FTSE is down to 5176 ( -69 from your 5245 exit point) and DOW to 10202 ( -163 from the hedge level).
So, long FTSE = -69 x £10 = -£690
short DOW = +163 x £5 = +£815
ok? Or clear as mud?
good trading
jon
Do you do this based on a pure monetary value of the 2 instruments or do you look at the ATRs as well?
For example, why did you pick £5 for the DOW trade?
FTSE moves about 80pts a day but you have to be careful as DOW moves about 170-180pts a day.