In the Programming mode of gcalctool, you have a log
button, which calculates the logarithm, but how do I know what base it's using and how do I change it?
For example, how would I calculate the base 2 logarithm for 16?
In the Programming mode of gcalctool, you have a For example, how would I calculate the base 2 logarithm for 16? 


By default the log button calculates base10 logarithms (while the "ln" button does, of course, basee logarithms). To specify a different base, you use a "subscript":
By the way, I found this pretty easily by accessing gcalctool's help (press F1) and looking for logarithms in the index. 


You can also use the base change formula:


