Note (September 2026): An earlier version said the Library folder is hidden by default in Mac OS X 10.6; it…
Roman numerals use seven letters: I, V, X, L, C, D and M. The adding and subtracting rules, a 1 to 100 chart, step-by-step conversion, years like MMXXVI, where they are used today and the most common mistakes.
A year is a leap year if it divides by 4, except century years, which must also divide by 400. The three-step check, why 2100 is skipped, the 1582 and 1752 calendar changes, a 2000-2100 list, and the Excel 1900 bug.
The 24-hour clock numbers hours from 00 to 23, so 14:30 is 2:30 p.m. A full conversion chart, two quick tricks, what NIST and ISO 8601 say about noon, midnight and 24:00, and how to switch formats on phones, in Excel and in code.
A Unix timestamp is the number of seconds since 00:00:00 UTC on 1 January 1970. How to read it, tell seconds from milliseconds, convert it in Excel, Sheets, Python, JavaScript, MySQL and the shell, and what the 2038 limit means.
Note (October 2026): This article previously listed Knowify plans called Essential ($186 per user per month) and Unlimited, said Knowify…
Note (October 2026): Earlier text described soy protein as dangerous and pea protein as harmless in every case; both statements…
Note (October 2026): Earlier versions of this article described bounce rate as time spent on a page and said unique…
Note (October 2026): This 2021 article quoted outdated PMI membership and PMP-holder figures and said Prometric runs the exam in…
Note (October 2026): This guide previously advised cleaning any tracker band with 70% isopropyl alcohol; Apple says alcohol wipes should…
Note (October 2026): Earlier versions of this article told readers to share their login with family and coworkers, gave the…
To buy bulk t-shirts from a reliable supplier, order a sample first, check the fabric weight (GSM) and fiber-content label,…