The slide rule pictured shows 62, not 61, which is correct within the precision limitations and very close to the correct answer (62.1). It appears that whoever read the answer mistook the fractional markings between 6 and 7 for 10ths (.1), when they are actually 5ths (.2).

The Graphoplex slide rule I used in physics classes in France in the 1960's (and which I still have, although I haven't used it in decades) had a magnification attachment that allowed you to interpolate an extra digit of precision, as well as scales for squares, cubes, natural logs, trigonometric functions and more.

Slide rules have one advantage over electronic calculators in that they show a range of answers at once, which makes them much faster for quick planning purposes. The inexpensive quick calculators often given out as promotions by banks and financial planners, or at trade shows, are just special purpose slide rules.

Regardless of the format you download, if you want to play your compilation in most CD players (that is, not computer CD drives or MP3 players) you will need to burn audio CDs in CD-Digital Audio format (CD-DA).

MP3 (or Apple's AAC equivalent) files are great for listening from appropriate devices but they are not as good for burning CDs. MP3 is a lossy format which tries to adapt to the way the human ear hears sounds when compressing music, but you make the perceived sound worse when converting from a lossy format to CD audio because the information restored is not identical to what was removed originally.

What this means is that for archival purposes and for burning CDs you should use a lossless format such as flac, which is smaller than uncompressed WAVE files and allows you to attach metadata as tags.  Of course, if your original source is MP3, you are stuck with what you've got and won't be able to get any better quality from it anyhow.

There are a wide variety of free programs out there that will let you rip and burn CDs and convert between different audio formats, but for nearly all of this kind of thing, I use Easy CD-DA Extractor from Poikosoft  (http://www.poikosoft.com/ - 25 euros) which puts all the tools you need in one extremely convenient package and does it all as well as the best of the individual programs.

This is another approach which may be less elegant but is both cheaper and more flexible for occasional use:

http://www.byteccusa.com/product/adapter/BT-300/BT-300.htm

I have one of these and find it very useful because it works with any kind of drive and is small enough to keep in my "fixit" toolkit. Newegg sells the SATA/IDE version for $25 and an IDE only version for $16.