How does one interpret financial data for stocks listed on multiple exchanges?
First and foremost you need to be aware of what you are comparing. In this case, HSBC as traded on the NYSE exchange is not common shares, but an ADR (American Depository Receipt) with a 5:1 ratio from the actual shares. So for most intents and purposes owning one ADR is like owning five common shares. But for special events like dividends, there may be other considerations, such as the depository bank (the institution that created the ADR) may take a percentage. Further, given that some people, accounts or institutions may be required to invest in a given country or not, there may be some permanent price dislocation between the shares and the ADR, which can further lead to discrepancies which are then highlighted by the seeming difference in dividends.
The problem is that while there are a lot of statistics that can be created from basic market data such as prices and volume, along with the fundamentals of the company, I think that if you talk to 8 different day traders, you'll get 12 different theories of how to interpret and trade based on those numbers.  Also quite likely, the more successful someone is at day trading, the more closely they are likely to guard their secrets and not want to divulge them. If there was any uniform concensus, they you'd see all the daytraders doing the same thing, and moving as a group, shortly after which you'd get 'contra' folks who would try to gain by moving in opposition, or 'predicta' folks who would try to front-run the pack. and.... (I think you can see where this leads)  A better idea might be to just work on educating your-self firstly with regard to nomenclature and terms, and then move on to reading some stuff about how markets work   etc.  I'd suggest starting with a book like 'Wall Street Words' and/or 'A Random Walk Down Wall Street' since both are great introductions to things, and move on from there.  Note that both of those books have gone through multiple editions, so be sure to get the most recent one (especially if you are trying to save money and buy a used version)   You are also likely to find an nearly endless supply of 'seminars' that will offer to teach you somebody's proven method for a fee, or for 'free' but after which you find our you need to use their special tools or data sources etc (which cost money) to use their 'system'  (either of which makes me think that their system can't be that great if they figure it's a surer thing to charge for 'teaching' or 'tools/services' than it is to use their system, otherwise they'd just shut up, practice what they preach and make money that way instead)  It might be worth attending the free ones just to get exposure to someone's theory on how to game the system, provided you are 'not an easy mark' and can withstand the high pressure sales pitch for their books/software/services etc that pays their bills and almost invariably comes along with such a seminar. ETFs are legally required to publicly disclose their positions at every point in time. The reason for this is that for an ETF to issue shares of ETF they do NOT take cash in exchange but underlying securities - this is called a creation unit. So people need to know which shares to deliver to the fund to get a share of ETF in exchange. This is never done by retail clients, however, but by nominated market makers. Retail persons will normally trade shares only in the secondary market (ie. on a stock exchange), which does not require new shares of the ETF to be issued. However, they do not normally make it easy to find this information in a digestible way, and each ETF does it their own way. So typically services that offer this information are payable (as somebody has to scrape the information from a variety of sources or incentivise ETF providers to send it to them). If you have access to a Bloomberg terminal, this information is available from there. Otherwise there are paid for services that offer it. Searching on Google for ETF constituent data, I found two companies that offer it: See if you can find what you need there. Good luck. (etfdb even has a stock exposure tool freely available that allows you to see which ETFs have large exposure to a stock of your choosing, see here: http://etfdb.com/tool/etf-stock-exposure-tool/). Since this data is in a table format you could easily download it automatically using table parsing tools for your chosen programming language. PS: Don't bother with underlying index constituents, they are NOT required to be made public and index providers will normally charge handsomely for this so normally only institutional investors will have this information. In general, how does a large open market stock sale affect prices? A very general answer, all other things being equal, the price will move down. However there is nothing general. It depends on total number of shares in market and total turn over for that specific shares. The order book for the day etc. What is the maximum percentage of a company you could sell per day before the trading freezes, and what factors matter? Every stock exchange has rules that would determine when a particular stock would be suspended from trading, generally a 10-20% swing [either ways]. Generally highly liquid stock or stock during initial listing are exempt from such limits as they are left to arrive the market price ...  A large sell order may or may not swing the price for it to get suspended. At times even a small order may do ... again it is specific to a particular stock. "Gnucash is much more designed for accounting than for budgeting. While it does have some simple budgeting features, they're largely based around tracking how much has been spent in the Expense categories/accounts, and seeing how close one is to a limit that's been set. Because the point of Gnucash is accounting, there's not a way to track an expense in two expense categories simultaneously. (You can split a transaction across multiple categories, to have a grocery store purchase of $150 be split across $100 Food and $50 Phone Minutes or whatever. But not have a $150 purchase be tracked as $150 Food and $150 Household expenses, because that's not how double-entry accounting works.) The closest way to do what I think you're looking for is to take advantage of the hierarchical account structure, and repeat subcategories as needed. For example: This would allow you to see Household expenses vs. Vacation expenses, and still see what it got spent on. Reporting on all ""Food"" purchases, if you want to do so, is slightly more tricky as you'd need to select all those ""Food"" categories separately in your report, but it's possible. You speak about wanting to ""track"" expenses multiple ways, so I think that this would allow you to record data sufficient to ""track"" it. But the point of tracking any data is to be able to report on it in some fashion, so if you have more specific reporting requirements, you might want to ask about that as well." A stock is only worth what someone is willing to pay for it. If it trades different values on different days, that means someone was willing to pay a higher price OR someone was willing to sell at a lower price.  There is no rule to prevent a stock from trading at $10 and then $100 the very next trade... or $1 the very next trade. (Though exchanges or regulators may halt trading, cancel trades, or impose limits on large price movements as they deem necessary, but this is beside the point I'm trying to illustrate). Asking what happens from the close of one day to the open of the next is like asking what happens from one trade to the next trade... someone simply decided to sell or pay a different price.  Nothing needs to have happened in between. From every article I've encountered, the chicken and egg aspect suggests that IV is produced by looking at options pricing, and calculating the IV from that.  The implication is that whatever is known at that time is included in the price. And that when you see a particular option trade an unusual number of contracts at a given price, the implication is that someone thinks they know something that's not already priced in, i.e. that the current price is not accurate, they can profit on the future event. "In the US, stocks are listed on one exchange but can be traded on multiple venues.  You need to confirm exactly what your data is showing: a) trades on the primary-listed exchange; or b) trades made at any venue. Also, the trade condition codes are important.  Only certain trade condition codes contribute towards the day's open/high/low/close and some others only contribute towards the volume data.  The Consolidated Tape Association is very clear on which trades should contribute towards each value - but some vendors have their own interpretation (or just simply an erroneous interpretation of the specifications). It may surprise you to find that the majority of trading volume for many stocks is not on their primary-listed exchange.  For example, on 2 Mar 2015, NASDAQ:AAPL traded a total volume across all venues was 48096663 shares but trading on NASDAQ itself was 12050277 shares. Trades can be cancelled.  Some data vendors do not modify their data to reflect these busted trades.   Some data vendors also ""snapshot"" their feed at a particular point in time of the data.  Some exchanges can provide data (mainly corrections) 4-5 hours after the closing bell.  By snapshotting the data too early and throwing away any subsequent data is a typical cause of data discrepancies.   Some data vendors also round prices/volumes - but stocks don't just trade to two decimal places. So you may well be comparing two different sets of trades (with their own specific inclusion rules) against the same stock.  You need to confirm with your data sources exactly how they do things. Disclosure: Premium Data is an end-of-day daily data vendor." I don't see it in any of the exchange feeds I've gone through, including the SIPs. Not sure if there's something wrong with Nasdaq Last Sale (I don't have that feed) but it should be putting out the exact same data as ITCH.