I may be seriously out of date, but "order of magnitude" was (c.1990s, and again, pedantically) the nearest power of 10. This is the way we taught it as well (

I may be seriously out of date, but "order of magnitude" was (c.1990s, and again, pedantically) the nearest power of 10. This is the way we taught it as well (those estimation problems in the first chapter of your physics text). Conversationally it was used more with a "wild ballpark" meaning. We would say "of the order of 3000" but strictly 3000 was of the order of 1000. 5000 was of the order of 10000. Etc.