Scan Engines are designed to find charts with a specific set of technical criteria on a specific date. Occasionally, we get a question from someone who is trying to use the scan engine to find stocks with a specific set of technical criteria over a range of dates. We call this the "within" problem since they are looking for something that happened "within" a certain time period. For example, "Show me all the stocks that had a MACD crossover within the past month."
The reason our scan engine doesn't support these "within" scans is because you cannot use them in a real-world trading environment. From a high-level perspective, the purpose of scanning is to develop scans that can help you decide which stocks to buy or sell "soon" - i.e. before the data used in the scan changes significantly. The standard scenario is to run your scans after the market closes in preparation for placing orders early the next day. While some of the results from a "within" scan may still be valid, others results may have become invalid by the time the scan is run and, what's worse, you cannot easily tell which is which.
We strongly recommend refining a "within" scan so that it refers instead to "today". For example, take the scan above and turn it into "Show me all the stocks that had a MACD crossover today." You can then use the "Starting" field (at the top of our scan interface pages) to see the results of the scan on any previous day you choose.
Using your same rationale, the OR logic, & a little extra typing, one can also create scans for a certain few days - like 1 day ago OR 2 days ago OR 3 days ago... etc. The only reason for desiring to scan a time-span many days ago is for back-testing... and the SC scanner is the wrong tool to use for that.
I usually scan in the last 3 days because it frequently takes a few days for an indicator to be confirmed by other data.
Posted by: C. E. Anderson | March 03, 2009 at 09:21 AM