CONSTELLATIONS BY SEASON
the northern evening sky through the year: 28 constellations per the Yale Bright Star Catalogue, latitude 40° N, evenings near 9 pm
METEOR SHOWERS
the twelve principal showers of the year · periods, peaks and ZHR per the IMO calendar
SPRING AND NEAP TIDES
the Earth–moon–sun geometry that makes the tides swing — after NOAA
BLOOD PRESSURE CATEGORIES
the six AHA categories · 2025 guideline · the higher of the two readings decides
CPR AND CHOKING
the 2025 American Heart Association algorithms, step by step — bystander, trained rescuer, and choking at three ages
DRESS CODES
six lines that turn up on an invitation, and what each one actually asks for — after Debrett’s
THE CHILD IMMUNIZATION SCHEDULE
Table 1 of the CDC schedule, by age: all twenty rows from birth to 18 years, United States, 2025
MAGNESIUM COMPOUNDS
the share of magnesium in the salt, computed from the formula · and what human trials measured
NAIL SHAPES
eight shapes at one scale · what tells them apart in millimetres
SERUM ACTIVES
when to apply, what to keep apart in time, what the season changes
THE STAGES OF SLEEP
light, deep and REM as honest shares of the night — and the 90–110 minute cycles it is built from
CSS GRID
the container properties and the item properties per the css-grid-2 specification — and what each does to the layout
BITS, BYTES, KILOBYTES
two scales · 1000 and 1024 · why a drive looks smaller
THE DMX512 PROTOCOL
512 channels down one serial wire, and why a full universe cannot refresh faster than 44 times a second
EAN-13
how thirteen digits become 95 modules of bars and spaces
FILE DESCRIPTORS
Three levels between a number and a file: what two numbers of one description share, what two descriptions do not — and where the offset lives
FILE LOCKS
A lock lies on a range of bytes, it has two different kinds of owner, and it guards no byte at all
FILE PERMISSIONS
Nine bits in three triads, three special bits — and why r and x on a directory are different powers
CSS FLEXBOX
main axis and cross axis · which property belongs to which
FLOWCHART SYMBOLS
10 shapes, and one algorithm drawn with them
![FILENAME EXPANSION: *, ?, […]](/api/img/cmsp2eg3h001q2dpdnyxkt8mu)
FILENAME EXPANSION: *, ?, […]
A leading dot and a slash disappear only in filename expansion: the same pattern “*” is seen by case, but not by expansion itself
GO vs RUST
seven questions, the same to both, and the document each answer is written in
HERE-DOCUMENTS
The body reaches the command as a single word, and one quote in the delimiter decides whether it arrives as typed
HTTP STATUS CODES
five classes · twenty codes you meet every day
IFS AND FIELD SPLITTING
Two kinds of delimiter: white ones merge into one, non-white ones each cut on their own — and the same value gives one field or four
JAVASCRIPT vs GO
seven questions, the same to both, and the document each answer is written in
JAVASCRIPT vs RUST
seven questions, the same to both, and the document each answer is written in
LANGUAGE CODES
487 rows in ISO 639-2; 183 languages also have a two-letter code and 20 have two three-letter ones — and the tag is always the shortest
LIFE CYCLE MODELS
the same steps arranged five ways: the document, the year, and what one turn of the loop covers
${…}: FOUR MODIFICATIONS
The colon asks about emptiness too: in the column of the empty variable it changes the answer four times out of four, and in the other two columns none
POSIX SIGNALS
Twenty-seven signals, five default actions — and two that cannot be caught, ignored or blocked
PYTHON vs GO
seven questions, the same to both, and the document each answer is written in
PYTHON vs JAVASCRIPT
seven questions, the same to both, and the document each answer is written in
PYTHON vs RUST
seven questions, the same to both, and the document each answer is written in
read: A LINE INTO VARIABLES
The last variable takes the whole rest of the line, inner spaces and all; without -r the backslash disappears, and a line with no final newline gives status 1 — although the variable is already full
THE SELECT STATEMENT
8 clauses in the order you write them — and the order they take effect in
THE UMASK
The file mode creation mask: the nine bits it clears, five arguments that name opposite things — and why umask 022 is not chmod 755
THE UNICODE SPACE
1 114 112 code points in 17 planes: 159 866 characters, 137 468 private, 814 730 free
UUID
thirty-six characters: where the version sits, where the variant sits, and what each of the eight versions is made of
VIDEO CARRIERS
nine formats at true scale — and the frame that kept growing after the carrier stopped
VIDEO FORMATS
who published each standard, when, the names it goes by, and what has to be squeezed
WORD EXPANSION
Four steps in a fixed order — and only two of them can change how many fields reach the command
GREEK ALPHABET
24 letters · names and where science uses them
BENFORD’S LAW
the first digit of a number: why a one turns up more than six times as often as a nine, and in which sets that is true
THE BIRTHDAY PARADOX
how many people it takes for two of them to share a birthday — and the same count for codes and fingerprints
REPEATING DECIMALS
which fractions stop, which run for ever, and how to know the length of the repeat without dividing
TN, VA, IPS AND OLED
what differs inside the cell · and a paper describing each mode
THE FUJITA SCALE
six categories of tornado damage — and the two different winds assigned to them