Scanning

dhall6938

Recently, I have noticed that the scans are not always consistent with what is shown on my charts. I have an intra day service with SC that is supposed to update every few seconds. I have noticed that the scans do not select anything for the first few minutes ( 3 to 5 minutes AFTER the open ) so I assume that the data information takes a few minutes to work with the scans. Having said all of that, I have noticed that my scan sporadically select a ticker all day long even though the chart says that it should meet all of the criteria in the scan. SC will no longer answer questions and I just can't figure out why the scans don't match the charts? As an example, this scan chose RUT early in the day but throughout the day, it would sporadically chose RUT or not chose RUT even though the MACD Lines never reversed back up all day long.

[Favorites list is 9] and [This week's MACD Line(12,26,9) > 0.0] and [This week's MACD Line(12,26,9) > This week's MACD Signal(12,26,9)] and [This week's MACD Line(12,26,9) < Last week's MACD Line(12,26,9)]

and [Today's MACD Line(12,26,9) > 0.0] and [Today's MACD Line(12,26,9) < Today's MACD Signal(12,26,9)] and [Today's MACD Line(12,26,9) < Yesterday's MACD Line(12,26,9)]

Maybe I don't understand how the scans work or maybe my computer browser or software are not compatible with the SC scans or maybe something else is wrong?

David

markd

Well, just to be clear, Stockcharts does not support scanning of intraday indicators - for instance, you can't scan for an hourly MACD crossover. The scan engine does not store intraday data for scanning. I see your scan does not ask for intraday conditions, so that's not the problem.

Second, scans work best when all your scan conditions use the same time frame - all daily, all weekly, etc. If you write a scan that mixes time frames, you don't get an error, but when you check the results, you have to be very careful. First of all, no chart will display more than one time frame. So, to verify the results of a scan with a daily condition and a weekly condition, you have to look at the daily chart and then the weekly chart.

Third, scans work best when you run them after the close for the time frame you are using. When I say "work best", I mean they are "easiest to verify". So, a scan with daily indicators will work best after the market close. A scan with weekly indicators will work best after the Friday close.

All that said, the scan engine does allow you to run any scan intraday. When you do that, the scan engine considers the data from the most recent update, say 1:03 pm, to be the closing data for any time period you are scanning for - so daily close for daily indicators, weekly close for weekly indicators, etc. MACD is based on the close, so even if the close at say 10:20 am would have triggered a hit for your scan, at 1:03 it might not, and, it doesn't look back to see if there has been a close to trigger the hit.

Another thing to keep in mind is, updates are frequent. This has several possible consequences. Depending on when and how long the scan takes to run, it may end up using data from more than one update (I don't know this for a fact - I don't work there) for the same scan. Also, by the time the scan results are returned and you get at chance to check them, the charts you use to verify the results will have been updated with new data, so what you see on the screen is not what the scan engine saw when you ran the scan.

dhall6938

Thank you for your response. I understand everything that you said except for what you said in your last two paragraphs. I'm confused. In my mind, as long as the weekly requirement is met ( as long as the weekly does not exceed last Friday's close ) all day long and the daily requirement ( as long the daily does not exceed yesterday's close ) are also met all day long, the scan should produce the same results every single time that I run the scan. FYI, when I separate the weekly and daily, I still don't get the results that I am wanting to see. I don't want to wait until after the market close, I want to see good results throughout the day. As an example, all of the requirements of the above scan have been met all day long today but it is not selecting RUT every time that I run the scan this morning. Odd and not what I need

dhall6938

You said......When you do that, the scan engine considers the data from the most recent update, say 1:03 pm, to be the closing data for any time period you are scanning for.

Can you define what your update is? Is it when I run a scan? Is it something internal at SC? Maybe it's when they get data updates from their data supplier on their end?

markd

I don't know enough about the internal workings of the scan engine to tell you more.

What did support say?

dhall6938

SC support will not discuss it with me. They referred me to here. Can I ask you a question in an effort to understand better what you have tried to tell me? Lets say that I want to scan for a line ( macd fline ) to go down below yesterday's close. At the first time it goes lower the scan will select it but if the price runs up above the level that the scan first selected it, even though the mack line is still below yesterday's, it won't select it again until it makes another new low?

markd

Well, that's part of the internals - the rules of the scan engine for managing traffic - that I have no direct knowledge of.

The process for intraday alerts is explained here

https://stockcharts.com/docs/doku.php?id=alerts#alert_processing

I don't know if multiple intraday scans are processed in a similar fashion.

I guess it's worth keeping in mind that the scan engine probably isn't optimized for continuous intraday scanning. It's designed to find symbols that meet certain criteria, not to track the progress of a symbol already selected. I know it's a bit of a fine distinction. In other words, I think the designers envisioned that you would get a scan hit, then view the chart, and if it's right, monitor the chart until entry. Your approach seems to be to use the scan engine to monitor the chart. Nothing wrong with that, just a little different from the intended use, I think.

So, while they do provide intraday data on charts with 5 second refresh (at the Pro subscription level), its not really an ideal platform for day trading, if that's what you are doing.

dhall6938

Mark, thanks again very much. I am not day trading any longer. I do understand that my scan signals are an eod thing but I want to enter them before the eod. And, it sounds like I may miss one if I don't happen to run the scan at the precise moment when the scan is in the mood to select one for me. I do have the Pro subscription so that I can run charts and scans all day long and I just recently noticed that the charts and scans are not always acting together. I'm not using the scan engine to monitor charts but I have been using charts to monitor the scans, after I noticed what I thought was a discrepancy between them. I think that I am starting to understand that even if one of my stocks meet the scan criteria, the scan may not select it depending on other factors related around data and data updates etc. Again, thanks for taking the time to try and help me understand what in the heck is happening. I was starting to wonder if my computer was screwed up

dhall6938

Mark, I don't mean to beat this horse to death but the link you gave me was for alerts. However, I will begin to search SC site for how scans may work. Thanks

dhall6938

Mark, look at what I found. I may have found something that will fix my issue. On all of my scans, I have selected the intra day update thinking that would give me the fastest information possible. I will select last market close now and see what happens.

The first update for the Scan Engine usually begins at 9:31 AM Eastern Time. Because of the vast amounts of data involved, all scanning systems work with datasets that are slightly older than “real-time.” When the market is open, our Scan Engine is continually updating the final data point for all of the stocks and indexes that it tracks on a rotating basis. When an Extra or Pro member runs a scan based on the “Last Intraday Update”, the Scan Engine will use a final daily data point that may be up to three minutes old, depending on when the scan is run.

markd

I sent you the "alerts" link because it runs scans intraday. I was speculating that if you run the same scan repeatedly intraday, the scan engine may use the intraday alert rules to process it. But I don't know that.

It appears the charts are updated continuously while the database for the scan engine is updated every 3-5 minutes. I ran your scan in one browser window with the chart on 5 second refresh in the other. The scan results didn't match the chart readings (you can get a data value by using the "rank by" statement at the end of your scan, e.g. rank by MACD Line(12,26,9) ) - which of course were fluctuating, while the scan results were static until the next update a few minutes later.

dhall6938

Just ran a couple of my scans using yesterday's close and so far that doesn't seem to help much either. Thanks again.

dhall6938

When an Extra or Pro member runs a scan based on the “Last Intraday Update”, the scan engines will use a “most recent” data point that is somewhere between 5 and 30 seconds old, depending on when the scan is run.

I think that this means that the scan engine uses the " most recent" data point as the last close so to speak. So, for the scan engine to make my selection again during the day the data point has to move beyond the last intra day data point that met the scan criteria. Whew. If that's true and I finally understand what is going on, it might be easy to miss something. Seems as though I would have to run the scan at the exact right moment

markd

I'm not sure whether your conclusion is correct. But, I think I would take to heart that the scan engine was not designed for the purpose you want to use it for, so it's not likely to be completely satisfactory - sort of like using a hammer to drive a screw - it will do it, more or less, but it's not really the best way.

dhall6938

Agreed Mark. Thank you for your time. You did help me work thru an issue that has been making me nuts. Wished that I knew of another service that actually did do what I want. Having said that and after thinking about it all day today, I may be able to make this work anyway.