Just an old time-tested (as opposed to back-tested) rule of thumb. To reiterate, SUR has gap, unfilled for weeks. For me, it's a moat.
Don't follow that one trades less than 100k a day, except somebody bought a bunch of it. That looks like somebody might know something. For what it's worth, the data I am posting in the post is for intra-day trading only.
I wouldn't expect you to follow. Merely used as an example. Aside from the spike on the break, nice and quiet. Note the word nice. Regardless of intra-day, day, week, month, or buy and hold., thee open is still thee open. At times it has an underlying agenda. "A specialness" to it. Intra-day is where I scratch trades. informally after 3 hours, otherwise at close.
SPY comprised from 500 issues and should mirror the underlying index. Each issue has a specialist. Individual issues open in accordance with alibis (if any). A material gap would reflect multiple axes acting in concert. I don't feel gaps can be predicted rendering a gap probability calculator or frequency distribution (regardless of quantity of samples) coincidental at best. Pre-market indications and "fair value" just shills to move paper. Note I previously used the phrase "amateur hour". Probability? The element of surprise is just one of the arrows in the axe's quiver.
Don't you ever read the news on why something gapped on heavy volume? CNA Financial to buy CNA Surety CHICAGO (AP) -- Insurance company CNA Financial Corp. said Thursday it will buy all the outstanding shares of CNA Surety Corp. for $26.55 in cash. http://finance.yahoo.com/news/CNA-Financial-to-buy-CNA-apf-2043101788.html?x=0&.v=1
"Y"??? Price explains news not news explains price. Yep, I seldom read news. Price tells me there's an alibi (whether genuine or contrived). Gap was 3 points below the offer and drew out 3 million shares (the spike). A miniscule proportion of the float. 3 million that didn't think $26 1/2 would materialize. From a time value standpoint, it's worth a 6 month wait for a "sure" 3 points per 100 shares. That 3 million shares was inventory for the ax to peddle back up to where it is. He hasn't unloaded all he acquired. Still have my moat and a reasonable profit. Situated quite well, TY. Incidently, SUR was previously spun off........FROM CNA. A tender is a tender. The fat lady hasn't sung yet. You just won yourself a trip to land of ignore, with your pithy little one-liner, FH