Division, the Hard Way

Monday, October 6, 2008

John Walkenbach recently posted Spreadsheet in a Phone, where he mentioned a new spreadsheet for the iPhone/iPod Touch. Well, I thought that this is the coolest thing ever, particularly as I just bought an iPod Touch (2nd generation) for my trip to the Financial Education Association meeting in Hilton Head. So, even though it isn’t free ($7.99) I headed straight to the App Store to buy a copy.

When I got there I saw that there were a few comments, and they weren’t too flattering. It seems that the Spreadsheet for the iPhone was released before it was ready for the masses (someone might think that Softalk is a division of Microsoft, but apparently that isn’t true). One small problem for some is that, at first glance, this spreadsheet can’t divide properly. One reviewer actually had the gall to complain that =3/2 returns 1 as the answer, and 2/3 returns 0. Imagine that…

Fortunately, another user helpfully pointed out that the spreadsheet can divide properly, if you know the correct formula. Apparently it understands logarithms and subtraction pretty well, so you can use this:

=POWER(10,LOG10(A1)-LOG10(A2))

So, if A1 contains 3 and A2 contains 2 then we find that 3/2 = 1.50. That works in Excel 2007 as well. And my students wonder why I’m always complaining that they don’t understand how to use logarithms. Now they know.

I really want to buy this thing, but I think that I’ll wait until the next version comes out. When it does, I’ll do a review here. It really does sound worthwhile, and they are building Excel compatibility into it.

I hope that the good folks at Softalk don’t mind me having a bit of fun at their expense.

Posted by .(JavaScript must be enabled to view this email address) on 10/06 at 01:08 AM

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“=POWER(10,LOG10(A1)-LOG10(A2))”

That’s how slide rules divide, if there’s anyone around who still remembers doing real work with one. My first calculator was a Texas Instruments Slide Rule something-or-other, presumably because it relied on this kind of logic.


Posted by Jon Peltier on 10/06 at 06:04 AM | #

Jon, was that a TI-30 by chance? The owner’s manual describes it as an “electronic slide-rule calculator” on the cover.

I’ve never owned a slide-rule, but I have thought of buying one several times. Seems like it would be fun to play with.

The first calculator that I, vaguely, recall owning was some kind of a paper or plastic thing with a stylus. IIRC, you would place the stylus into a hole in a column and pull it up or down. That is about all that I remember. Somehow, it was able to do addition, subtraction, multiplication and division. Probably based on some logarithmic scaling.


Posted by Tim on 10/06 at 11:53 AM | #

I don’t recall the exact number, but I think it’s earlier than the TI-30. More like the SR-50. When I went to college I got a new TI-59. Both are seen in this page:

http://www.thocp.net/hardware/ti_calculators.htm


Posted by Jon Peltier on 10/06 at 12:14 PM | #

That is a great page. I remember those days, when “electronic calculators” were far too expensive for my family to buy one (I was 11 in 1974 when the SR-50 came out). The cool thing about that page is that it gives the original prices.

The Bureau of Labor Statistics has an inflation calculator that can be used to see the inflation-adjusted price in today’s dollars. The SR-50 came out in 1974 at $169.95. That equates to $755.25 in today’s dollars. Wow!

In the late 1980’s I had an HP calculator that did nearly everything, including symbolic math. I don’t recall the model or price, but I don’t think it cost even $169.95 at the time. It is amazing how much improvement there has been in electronics and how much prices have declined.


Posted by Tim on 10/06 at 12:55 PM | #

Geez, I did math before calculators were invented. wink


Posted by Debra Dalgleish on 10/06 at 08:04 PM | #

I had a great HP engineering calculator that I used from the late 80s to the eraly 90s. I still have it, but hardly use it since I’ve become dependent on Excel for my math.


Posted by Jon Peltier on 10/07 at 06:42 AM | #

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