Do query services like Google Finance and Yahoo Finance go back to correct busted and adjusted trades?
No. Busts are very infrequent, and if an equity were illiquid enough to be affected, the bust cost would be enormous. For a liquid equity, the amount of busted volume is insignificant except during a flash crash or flash spike.  Then it would be reasonable to redownload.
It looks like GOOG did not have a pre-market trade until 7:14 am ET, so Google Finance was still reporting the last trade it had, which was in the after-hours session yesterday. FB, on the other hand, was trading like crazy after-hours yesterday and pre-market today as it had an earnings report yesterday. I use Yahoo Finance to plot my portfolio value over time. Yahoo Finance uses SigFig to link accounts (I've linked to Fidelity), which then allows you to see you exact portfolio and see a plot of its historical value. I'm not sure what other websites SigFig will allow you to sync with, but it is worth a try. Here is what the plot I have looks like, although this is slightly out of date, but still gives you an idea of what to expect. Log-returns are very commonly used in financial maths, especially quantitative finance.  The important property is that they're symmetrical around 0 with respect to addition. This property makes it possible to talk about an average return. For instance, if a stock goes down 20% over a period of time, it has to gain 25% to be back where you started.  For the log-return on the other hand the numbers are 0.223 down over a period of time, and 0.223 up to get you back to square 1. In this sense, you can simply take an arithmetic average and it makes sense.  You can freely add up or subtract values on the log-return scale, like log-interest rates or log-inflation rates.  Whereas the arithmetic mean of (non-log) returns is simply meaningless: A stock with returns -3% and +3% would have 0% on average, when in fact the stock has declined in price? The correct approach on direct price-returns would be to take a different mean (e.g. geometric) to get a decent average.  And yet it will be hard to incorporate other information, like subtracting the risk-free rate or the inflation rate to get rate-adjusted average returns. In short: Log-returns are easier to handle computationally, esp. in bulk, but non-log-returns are easier to comprehend/imagine as a number of their own. "No, I understood your question perfectly.  I'm just saying that sort of situation is generally rare.   A quick Google search yields [this article] (http://www.investopedia.com/financial-edge/1112/small-business-financing-debt-or-equity.aspx) which responds to the question - Which funding method should I choose? with the answer ""Often you will not have a choice"".    That is exactly what I'm saying.  The status and stage of your business dictates what sort of financing is even available to you.  Most often you don't even have a choice between one or the other.  If you want a formula, the other people responding mentioned [WACC] (http://www.investopedia.com/terms/w/wacc.asp) which is the ""standard"" that finance professionals typically use.  You generally will want a WACC that is similar to other successful companies of your similar size and industry.  The actual mechanics of adjusting your WACC will involve either issuing (or repurchasing) equity or debt.  Regardless, what you are asking is not generally practical nor does it come into practice in 99 out of 100 financing situations.  WACC is important to understand and consider but people don't issue equity or debt just to balance their WACC.     Think about this another way... how easy is it to raise debt?  Probably fairly easy as usually you can go to commercial banks or go to an investment bank if you're raising enough debt.  Companies borrow all of the time, they're constantly paying off loans or taking new ones with different interest rates.  There are revolving lines of credit, secured loans, factoring (borrowing against receivables), EETCs, fixed interest debt, variable interest debt, mezzanine debt, etc etc.  How easy is it to issue equity?  Pretty amazingly difficult... sure you have your IPOs but that happens once in a company's lifetime.  You might have [secondary offerings] (http://en.wikipedia.org/wiki/Secondary_market_offering) or [follow ons] (http://en.wikipedia.org/wiki/Follow-on_offering) but those are incredibly rare... I mean you've probably never even heard of them right?  You don't hear about Apple or Boeing doing those every quarter do you?  You'll hear about private equity companies buying up firms and you'll hear about mergers all of the time but again those are once-in-a-company's-lifetime events.    So now that you've read that.. how often is a company **really** going to be deciding between debt and equity?  Not very often." thanks.  I have real time quotes, but in the contest, if you put in a market order the trade might happen at the delayed quote price and not the real time price.  Does anyone know at which price it will trade, delayed or real time? The yahoo finance API is no longer which broke the Finance:Quote perl module.  The Finance:Quote developers have been quick to fix things and have produced several new versions in the last week or two.  The short of it is that you need to update Finance:Quote, then obtain an AlphaVantage free key and tell Gnucash to use AlphaVantage as it's source for online quotes by editing your securities in the Price Editor. Sure, Yahoo Finance does this for FREE. Try Google Finance Screener ; you will be able to filter for NASDAQ and NYSE exchanges.