THE COLLATZ CONJECTURE
halve the even, triple the odd and add one: the road of 27, the record holders and a problem nobody has solved
THE DOOMSDAY RULE
the weekday of any date in the Gregorian calendar, worked out in the head in three steps
REPEATING DECIMALS
which fractions stop, which run for ever, and how to know the length of the repeat without dividing
THE RULE OF 72
the time it takes steady growth to double: the division you can do in your head, how far it misses and why the divisor is what it is
THE BEAUFORT SCALE
thirteen forces of wind — from water like a mirror to a wave of fourteen metres
COLOUR GAMUTS
sRGB, Display P3, Rec. 2020 and ProPhoto RGB on the CIE 1931 chromaticity diagram
THE COMPASS ROSE
the sixteen compass points with exact bearings: four cardinal, four intercardinal, eight in between
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
GREEK LETTERS IN SCIENCE
10 capitals with a shape of their own, 14 twins of Latin letters, and what each one stands for
USDA HARDINESS ZONES
the 13 zones by average annual extreme minimum — each range in °F and °C, with the a and b half-zones
THE MOMENT MAGNITUDE SCALE
what a single step hides: ×10 in recorded amplitude and roughly ×32 in released energy — drawn to true scale