The four rules
- Write the precision the number has. Thirteen days of compute means days rather than minutes. Writing it as 13.4 days would add a decimal place the underlying assumption cannot support.
- Write a range as a range. A window of three to twenty one days is two numbers and stays two numbers. Averaging it produces a figure that describes nothing anybody experiences.
- Write an order of magnitude as an order of magnitude. Where the honest claim is about a trillion attempts, the page says about a trillion, and prints the exact figure only where the arithmetic depends on it.
- Always attach the unit. Eight what. Forty what. A bare number is a rumour, and the sidebar of this site prints a unit beside every value for that reason.
Where the rules bite
Thirteen days of compute is a shape, not a schedule
The figure on the eight character prefix page comes from dividing about a trillion attempts by a rate somebody chose. The rate is an order of magnitude estimate, so everything downstream of it is one too. Thirteen days is the site saying days rather than minutes, and days rather than years.
Written as 13.0 days it invites a question about which day. Written as about thirteen days with the rate sitting in the spec strip, it invites the right question, which is whose hardware. Rented compute turns the same arithmetic into hours, and the page says so on the same screen.
A three to twenty one day window is not a twelve day delivery
Delivery windows are the clearest case of the second rule. A window of three to twenty one days is not a claim that parcels take twelve days. Almost nothing arrives at twelve. The distribution is lumpy, and the two ends of the range are doing different jobs. The low end is what is possible and the high end is where you stop assuming and start reading the dispute rules.
Collapsing a range into a midpoint destroys the exact information a reader needs. Somebody planning around twelve days has invented a deadline for themselves. Somebody who kept the range knows that day nine means nothing at all and day twenty two means something.
A fraction of a coin is not a price
A fee written as a fraction of a coin is a quantity of coin. It becomes a price only once a conversion rate is applied, and the rate moves while you are reading. This site writes such values in the unit they are actually denominated in and states what would have to be assumed to turn them into money.
That is also why no page here prints a figure in dollars or euros. The moment a currency symbol appears the number acquires an implied date and starts going stale, which is a different failure from being wrong and much harder for a reader to notice.
Precision and accuracy are different things
Precision is how finely a number is written. Accuracy is how close it sits to the truth. The two are independent, and confusing them is the most common way a figure gets dressed up beyond its evidence.
A worked example. Suppose you time an order and record that it arrived after 8.437 days. That is precise to three decimal places. If the clock you used was a timestamp on a message that sat in a queue for a day, the figure is also wrong by a day. Precise and inaccurate at the same time, and the precision is what makes it convincing.
Now suppose you write about a week and a bit. That is imprecise and accurate, because the true value sits comfortably inside it. Given the choice, the second statement is more useful and the first is the one that will get quoted.
The rule that follows is to round outward to the precision the evidence supports and then stop. When the input is an order of magnitude guess, the output is an order of magnitude answer no matter how many digits the calculator was willing to print.
What to do with a number that breaks the rules
Most figures quoted in this subject arrive with no unit, no range and no source. That does not make them false. It makes them unusable until three questions have answers: what is the unit, what was assumed, and how precise was the input.
A number that cannot survive those three questions is a rumour with a decimal point. That is not a reason to argue with whoever repeated it, since they probably received it the same way. It is a reason not to plan anything around it.
Everything published here is meant to survive the same three questions. Where a page cannot, it says so in its opening lines and carries the judged chip described on the counted and judged page. If you find a number here without a unit, or a range quietly turned into a single figure, that is a defect worth pointing at.
Questions people ask
Why not give an average delivery time?
Because an average over a lumpy distribution describes an outcome that rarely happens and hides the two facts that matter, which are the earliest plausible day and the day the dispute clock starts to matter.
Is rounding not just hiding detail?
Rounding to the precision the input supports removes digits that were never evidence in the first place. Keeping them would be adding detail rather than preserving it.
Why are large numbers written out in words here?
Because a reader takes about a trillion from a phrase faster than from a row of digits. The exact figure is printed wherever the arithmetic depends on it.