How to know when an author is using natural log? I was always taught that "log" is log base ten and "ln" is log base $e$, and there are plenty of sources that use this. But a lot of other sources use "log" as the natural log, and some books I have don't seem to specify which system they use and I can't quite figure it out sometimes. Is there a good way to know when somebody is using one or the other, or are there particular fields which tend to use one system or the other?
Just look for instances that give away which log they are referring to.

If you are using a precalc or a calc textbook, the chances that log refer to base 10 is slim to none.
Just look for instances that give away which log they are referring to.

If you are using a precalc or a calc textbook, the chances that log refer to base 10 is slim to none.