About: Why an Almanac

The Yardstick Almanac is a reference for one kind of question: why is it this number? Why does 2100 skip February 29? Why is the American yard defined by the meter? Why does the 1889 kilogram cylinder now carry an uncertainty of its own? Each answer traces a number back to the documents that fixed it and the choices made along the way.

Not that kind of almanac

The name uses “almanac” in its sense of a reference book of tables and reckonings to keep within reach. This site is not a farmers' almanac. It has no weather forecasts, no planting calendars and no lucky days. It is a measurement reference, organized into five sections.

Calendars & Time covers the rules behind dates: leap years, leap seconds, Old Style and New Style dates, and ISO week numbers. Units & Standards follows definitions through the documents that set them: the U.S. survey foot, the definition of the kilogram, the metric system in the United States and the nautical mile.

Scale & Estimation works through sizes and counts with the working shown: how far light travels in a nanosecond, how many people have a February 29 birthday, what the astronomical unit is, and what unit Eratosthenes' figure for Earth's circumference was counted in. Maps Explained looks at the measurements built into maps: the prime meridian, the WGS 84 reference system, and what a choropleth map is coloring. Reading Charts uses charts built from this site's own data to show how a chart can mislead: hours of daylight by latitude, misleading graphs and pie charts.

Who it is for

The main reader is anyone who has looked at a number and wondered who picked it. The site is also written for teachers and students who want scale comparisons, map measurements and chart examples they can check, for people who work with data and write about it, and for genealogists and history readers facing a record dated under two calendars.

Some readers will be better served elsewhere. There are no quick converters here (a page that only turns centimeters into inches is not this site's job), and no investment, interest-rate or price comparisons. Astrology, auspicious dates and the religious meaning of feast-day reckoning are not covered; calendars appear here as arithmetic and history. There is no advice on buying measuring instruments, and nothing on this site is a legal or compliance opinion about weights and measures.

Where the site stands

The tagline is Every unit is an argument somebody won. The working view behind it: a unit, a calendar or a map is a truce line in an old argument. Someone picked the reference, someone gave ground, and a small mismatch is often left over. The site's job is to find that mismatch and put it back on the table.

That view is a position, not a scientific claim. It applies to conventions people made: unit definitions, calendar rules, projection choices and the encodings of a chart. It does not extend to the constants of nature or to physical law.

Articles also take positions of their own, each with a stated limit, and each open to argument. The Gregorian leap-year rule of 1582 is good enough to leave alone; that position is about arithmetic and does not judge any religious calendar. The pie chart is not guilty: with two or three parts, where the point is each part's share of the whole, it is a sound choice. The defense has limits: past five slices, or when several groups are being compared, a different chart works better. A choropleth map shaded by raw counts mostly redraws where people live; without a denominator it should be a dot map or a map of rates. That critique goes after the chart and never names the person who made it.

If an argument here looks wrong, the address at the end of this page takes disagreements as well as corrections. Sources help more than opinions.

Three terms you will see

Three phrases are this site's own names for recurring ideas. They are labels coined here, not standard vocabulary, and each has a short definition page.

The remainder is the part a measurement convention leaves unmatched against the thing it was meant to fit, such as the fraction of a day that a calendar of 365 whole days leaves over each year.

The unstated per is the “per” a number or chart leaves out, such as per person, per year or per square kilometer; change it and the conclusion often changes too.

The frozen error is a historical measurement error that was later written into a definition and stopped being treated as an error.

How an article is built

Each article opens with a short answer under the headline, then a Calibration card: a small table of the defining facts, such as what a unit is defined as, since when, and in which document. The figures and tables that follow are drawn from data files you can download beside them. Each article ends with a line headed “Carry the remainder:” that names the mismatch the topic leaves over, or, where there is none, what the convention chose and what it gave up.

How the numbers are checked

The short version: primary documents come first, every major number carries a tag saying whether it is exact by definition, measured, estimated or disputed, and every date and conversion is worked out from the source values rather than copied. Dates are computed two independent ways, and the two results must agree. Unit conversions are done in exact fractions.

The full account, including the order in which sources are trusted and what each value tag means, is on Where the numbers come from.

The colors

The palette comes from field surveying. The dark green is the ink of a surveyor's field book, where readings get written down. The pale cream background is a boxwood rule, with the faint green grid of engineering paper. The occasional red is from the painted bands of a ranging pole.

When something is wrong

Errors are reported by email to contact@theyardstickalmanac.com. The “Report an error” link at the foot of every page opens the same address; there is no form. A useful report names the page, quotes the sentence and gives the source that disagrees with it. More on what helps is on Write in.

A substantive correction is logged in two places on the same day: in the corrections note at the end of the article, and on the public corrections log. Pages are not changed silently.