I have a Zeus book too, but have to admit I don't use it much these days.
I have a calculator and when I can't find that in the shavings a piece of paper/scrap wood and a pencil to multiply and/or divide by 25.4 - Is an on-line tool really needed for that?
I used to use the Zeus book for tapping drill diameters but then realized that the tapping drill for 60 degree threads is simply the nominal diameter less the thread pitch which is easy in both metric and imperial.
Jon