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The calculators usually use $\log x$, while articles on wikipedia and other websites often use $\log_{10} x$, finally the ISO-80000-2:2009 uses $\lg x$.

Which one of these is correct? Or at least expected? If there isn't one, is any considered incorrect or discouraged?

Is the convention varied by regions perhaps?

user1561358
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    See also https://math.stackexchange.com/questions/1499094/natural-logarithm-notation and https://math.stackexchange.com/questions/293783/when-log-is-written-without-a-base-is-the-equation-normally-referring-to-log-ba and https://math.stackexchange.com/questions/552038/are-base-ten-logarithms-relics and https://math.stackexchange.com/questions/2071963/should-the-notation-log-x-mean-the-decimal-logarithm and probably many, many more. – Gerry Myerson Nov 29 '17 at 08:21
  • See Common logarithm as well as Logarithm: Particular bases. – Mauro ALLEGRANZA Nov 29 '17 at 08:22

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Definitely not $\log(x)$. That is reserved for natural log. I would say use $\log_{10}(x)$.

Edit: This answer is more complete and correct. In computer science $\log(x)$ often means $\log_2(x)$. (Thanks also to @Qudit for mentioning this.)

littleO
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