1. "log" button: is to calculate log base 10 (known as Common Logarithm)
2. "ln" button : is to calculate log base e (known as Natural Logarithm)
now to calculate log base 2, you can use any of these two, but whichever, you gonna need to convert it into base 2.
You can do this by dividing your result by the "log" or "ln" of base 2.
If you to calculate log(x) base 2, then calculate log(x) base 10 then divide it by log2 or to calculate ln(x) base 2, do it with base 10 then divide it by ln2.
log8 base 2 is 3. using calculator is should be log8 base 10 / log2 .
thank you :)