Here's a challenge for you...

[krtxmrtz]

Mine can't do that either but you can force it to.
logb(n) = x
b^x = n
loge(b^x) = loge(n)
xloge(b) = loge(n)
x = loge(n)/loge(b), therefore
logb(n) = loge(n)/loge(b)
yay!

It's easier to read if you use tags to crete subindices. If you don't know how to use them, just click the quote button and see how I've implemented subindices in this post.

log_bx = log_zx / log_zb

where z is any number, but of course you want z to be either e or 10, which are the available logs in calculators:

log_bx = log₁₀x / log₁₀b
or
log_bx = log_ex / log_eb = ln x / ln b