Expert: Steve Holleran - 3/5/2007

Question
Hi,

I have a column of values which are log10. How can I work out what those values were before being "logged" i.e. what is the inverse of log10? I thought it was natural log but I've been told thats not right!

Answer
Hi Andy,

I hope I understand you correctly.

Any log expression which is written "log N" without a base being indicated are common logs, which are base 10.

So, if the expression is "log 10", it means

log(base 10) 10 , which is 1.

Another way to see it is call the unknown answer X

then log (base 10) 10 = X , and changing to an exponential expression, you have 10^X = 10 , so you can see X = 1.

Likewise, if you have log 10000, then 10^X = 10000 and X = 4, since 10000 = 10^4.

Natural logs are logs base e, and are written ln.

I hope this is what you were looking for.

Steve Holleran