New Year's Eve
New Year's Eve
[Cueball, with his hands raised, is talking to Megan and White Hat.] Cueball: Tomorrow is New Year's Eve, and you know what that means: Cueball: It's the one day of the year when you can convert between ages and birth years by subtraction without worrying about off-by-one errors! Cueball: Also there are probably parties.

This was the first of two New Year comics around the 2019-2020 New Year, the second being 2249: I Love the 20s .
An easy way to determine someone's age is to subtract their birth year from the current year. However, if their birthday has not happened yet that year, this calculation will predict them to be a year older than they actually are. By New Year's Eve , everybody's birthday has happened that year (or is happening, but legitimately tallied up), so this error will not occur. Cueball is excited by this, whereas most people would be more excited by the parties that typically occur around New Year's.
"Off-by-one" errors are commonly made in computer programming, especially by novices, when looping over sets of objects. They can also appear in everyday life. If one is given a range of numbers, such as {10, 11, 12, ..., 99, 100}, a common error is to assume that the number of numbers in the range is the first number minus the last number: 100-10 = 90. However, the correct answer is 91 since both endpoints are included in the set. This specific type of "off-by-one" error is called a fencepost error.
In the title text, Cueball suggests a New Year's Eve party with the theme of "off-by-one errors", saying it's challenging to build off of but that he's heard of worse. No information is given as to what such a party theme would entail, nor what could possibly be a worse party theme. (On the other hand, the parties depicted in 51: Malaria and 829: Arsenic-Based Life , based on themes of disease and poison, respectively, look much worse than an "off-by-one errors" party would likely be.)
The idea of off-by-one errors for a New Year's Eve party is inspired by the numerous discussions about the time when the next decade starts, whether 2020 or 2021. 2249: I Love the 20s also treats the subject directly.
[Cueball, with his hands raised, is talking to Megan and White Hat.] Cueball: Tomorrow is New Year's Eve, and you know what that means: Cueball: It's the one day of the year when you can convert between ages and birth years by subtraction without worrying about off-by-one errors! Cueball: Also there are probably parties.
