Reference
Market Basics and the Vocabulary Here
A price and a volume figure look like plain facts. Both are aggregates with conventions inside them, and every measure on this site inherits those conventions, so this is the section that states them.
The rest of this reference compares numbers against other numbers: a session’s volume against its recent average, a count of advancing issues against a count of declining ones, a range against the volume that produced it. All of that assumes the underlying figures mean what they appear to mean.
Mostly they do, with two qualifications that recur on every page. A quoted price is the last completed trade rather than a valuation. And a volume figure is an aggregate of several different kinds of execution, only some of which happen where the company is listed.
Three questions worth being able to answer
Not a test, and a useful check on whether the vocabulary has landed. Each one is answered somewhere in this section, and each one disposes of a family of claims that circulate widely.
Can volume show more buying than selling? No. The two are the same event counted once, so a volume figure has no direction of its own. Any measure that reports one has imposed a rule, and the rules disagree.
Is a quoted price a price you can get? No. It is the last completed trade. What you can get is the bid or the offer, and on an illiquid instrument those sit far enough apart that a difference between two closes can be an artefact of which side each print landed on.
Does an index at a new high mean most companies rose? No. A value-weighted index is dominated by its largest members, so it can make a new high while most of the list falls. That gap is the entire reason the breadth measures exist, and no index level or heatmap can answer it.
Four conventions that sit inside every figure here
Each of these is a decision somebody made about how to record a number. None is visible in the number, and each one changes what a measure computed from it can support.
The close comes from an auction. On most venues a closing price is set by a mechanism that matches accumulated orders at one price at a single moment, rather than being the last continuous trade. That is why the close is the price with the most agreement behind it, and why the volume that arrives with it is one print from a queue rather than continuous trading.
Prices may be adjusted or unadjusted. An adjusted series divides historical prices for splits and accounts for distributions; an unadjusted one does not, so a split reads as a collapse. Most providers offer both and default to one without saying which. The biggest-losers page shows what the unadjusted version does to a ranking.
Volume is signed by convention, never measured. Every measure that reports buying against selling has imposed a rule — by the close against the previous close, or by where the close sat inside the range — and the rules disagree about a substantial share of sessions. The volume page computes the disagreement.
Breadth counts include more than companies. An exchange's issue count contains funds, preferred shares, exchange-traded products and multiple share classes, several of which move together on interest-rate news. A count is still a count; it is simply not a count of businesses, which the advance/decline anatomy works through field by field.
When a session's numbers actually settle
A figure read at the closing bell is provisional, and the difference between it and the figure that stands the next morning is larger than most readers expect. Two mechanisms account for nearly all of it, and both matter whenever a day is compared against an average.
Off-exchange prints arrive late. Trades executed away from an exchange are reported to the tape within a fixed window rather than instantly, so a meaningful share of the day's volume is still being added after the continuous session ends. A total captured at 16:00 and a total captured at 17:00 are different numbers about the same day, and neither is wrong.
Prints get corrected. Erroneous trades are busted or amended, and the correction flows through to the consolidated total. The effect is small on a typical session and occasionally large on a disorderly one: which, again, is the session anybody actually wants to measure.
The practical rule is that a volume comparison should take both figures from the same source at the same point in its revision cycle. An intraday reading against a settled historical average will understate today by whatever has not yet been reported, and the gap widens exactly when a session is unusual enough to be worth looking at. The volume baseline page sets out how to build the average side of that comparison so the two halves stay consistent.
The two numbers everything else is built on
A price and a volume figure look like plain facts and are both aggregates with conventions inside them. These two pages set out what each one actually records, which is what makes the rest of this reference readable.
- The stock market and what a price isA quoted price is the last completed trade, not a valuation and not an offer. Who trades, where, and what the number can support.
- Why volume mattersVolume counts transfers, and every share bought was sold. What that symmetry rules out, and what it still leaves.
The historical record
The events the rest of the site refers back to, as a dated reference rather than a narrative.
- Stock market crashesThe major declines with their dates and depths, and what the volume and breadth data looked like through each.
- What a market summary should containThe five numbers a daily summary needs, and why the index level is not one of them.
- Bear marketsThe longer declines that were not crashes, duration rather than depth.
Where the two numbers get compared
Once the two basic numbers are clear, the rest of the site is about comparing them against something.
- A volume baselineThe comparison that turns a share count into a reading: today against the instrument’s own recent average.
- Market breadthHow many issues took part, the question no index level or heatmap can answer.
- Indicator libraryEvery measure, what it is calculated from, and where it is documented to fail.
Frequently asked questions
Who is this section for?
Anyone reading the rest of the site who wants the assumptions stated rather than implied. Every indicator page here takes for granted that you know what a price and a volume figure are, and both turn out to be aggregates with conventions inside them rather than plain facts. Nothing in this section is advice, and none of it expires.
What is the single most useful thing to understand first?
That volume is symmetric. Every share bought was sold, so a volume figure cannot tell you whether buyers or sellers were in control; it tells you how much stock changed hands. A large part of the published commentary on volume assumes otherwise, and recognising that assumption is the fastest way to filter what is worth reading.
Why does the site keep saying "consolidated volume"?
Because a single-venue figure is a fraction of the total. In the United States a security trades on many venues plus a substantial off-exchange share, all reported to one tape, and the primary listing exchange is frequently a minority of its own security’s volume. The figure on this page sets out that composition. Comparing a single-venue number with a consolidated one is the most common way two people end up disagreeing about a volume figure.
Is a quoted price a valuation?
No. It is the price of the last completed trade, which is a fact about one transaction between two parties who each thought it was a good idea. It is not what the instrument is worth, not the price you can transact at, and not an offer. The bid and the offer are the prices available; the last trade is history, and on a thin instrument it can be some time old.
Does a volume figure include after-hours trading?
The consolidated figure includes trades reported to the tape outside the continuous session, and data providers differ on whether the number they publish does. Extended-hours volume is a small fraction of a normal day on most instruments, and a large fraction on the day of an earnings release, which is precisely the session someone is most likely to compare against an average built from regular hours. Establish which window a figure covers before comparing it with anything.
Does the site cover options?
No, beyond noting where options activity affects the data this reference is about, monthly and quarterly expiries concentrate volume into known sessions, and index options are why some indices exist in the form they do. A proper options reference is a different subject with a different vocabulary, and a half-page on it would be worse than the honest absence.
Where should a complete beginner start?
With the two pages in the first group above, then the volume baseline page. Those three between them cover what a price is, what a volume figure is, and how to compare today’s volume against the instrument’s own history, which is the single most useful habit on this site and needs no indicator at all.
Is any of this specific to one market?
The mechanics described here are American, because that is where the published data and most of the research come from. The concepts transfer: every market has a last-trade price, a bid and an offer, a volume figure with reporting conventions, and an auction at the close. The specific proportions and the venue structure do not, and any figure quoted from one market should not be assumed to hold in another.