what about if amgn start move immidiately against you? (what usually happends))))you will need couple more sec to buy sec. leg. at this time you will be in about 0.5% loss. what you going to do in this situation? how big the difference between two stocks can be considered big enough? just trying to clarify few details.. thank you! p.s. i agree about hist. correlations))) some of my pairs been good for couple years, but in last few month,as i mentioned somewhere before-trends start show up. trends in totally different directions for 20-30, even 50%....good stocks,same products....but...that why i stop hold them for more than one trading session.