RESISTOR COLOUR CODE
the bands, the tolerances and the preferred series of two standards
ROCK CLASSIFICATION
the three classes, 24 named rocks and the cycle that links them — after USGS and NPS
THE SAFFIR-SIMPSON SCALE
five categories of hurricane wind — and how much more damage each next one does
SPECTRAL LINES
five gases on one wavelength scale, from the violet edge to the red
WHAT A TORNADO BREAKS
twenty-eight damage indicators — and the wind at which each one gives way
THE TREE OF LIFE
who sits inside whom · where animals, fungi and plants actually are
FLAG SEMAPHORE
two flags, eight positions 45 degrees apart — all 26 letters; after the numerals sign A–I read as 1–9 and K as 0
MARITIME SIGNAL FLAGS
the twenty-six alphabet flags of the International Code of Signals — and what each one means alone
NUMERAL PENNANTS AND SUBSTITUTES
how to fly the same flag twice in one group with only one set aboard
KNIGHT
the nearest square off the lines, over pieces, and four moves to the square next door
PAWN
one square forward, two on its first move, capturing diagonally — and never going back
MARTIAL ARTS FAMILY TREE
fifteen schools and thirteen lines of transmission — every arrow is a documented apprenticeship, not a legend
NEEDLES AND YARN
knitting needle sizes in three systems — metric, old UK, US — and the 0–7 yarn weights per the Craft Yarn Council
THE LARGEST COUNTRIES
the ten largest by surface area — as squares at true scale, each inside the next
LEAP SECONDS
27 seconds added to UTC since 1972, none since 2016 — the longest run there has ever been
PAPER SIZES
the A series · from A0 to A6
PHOTO PRINT SIZES
how many millimetres each size really is, and how much of the frame goes under the knife
CAMERA SENSORS
seven sizes at one scale, with the crop factor computed from the diagonal
SI BASE UNITS
seven constants given an exact number — and the seven units that follow from them
SI DERIVED UNITS
twenty-two with names of their own — and what each one is made of
SI PREFIXES
from quetta to quecto · twenty multipliers
THE AMERICAN WIRE GAUGE
forty-four sizes derived from two diameters and one law of progression
PETROL AND DIESEL
nine lines of comparison, and in three of them the requirement is the same for both