# Business card math tables -- for geeks only

Discussion in 'Electronics Resources' started by someonesdad, Nov 4, 2009.

1. ### someonesdad Thread Starter Senior Member

Jul 7, 2009
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A couple of weeks ago I was fiddling around with a software idea (IIRC, something to do with functional programming) and wound up generating a simple, small logarithm table. Then the idea hit me that little tables like this could be useful in a business card size. I made up some of these tables and wrote up a document on their use, as it's possible that the folks who grew up with calculators have little to no experience doing manual calculations using tables.

You can find the document here.

Note I am not advocating a return to those old methods of calculation, which were just plain drudgery. However, we technical folks sometimes need to make numerical estimates and these tables might be of help when a calculator isn't handy. I always carry a little home-made notebook with me and I pasted eight of the tables into the back two pages of the notebook (log/antilog, sin/cos, squares/reciprocals, and square roots) so they're handy when I need them.

Truth in advertising: manual calculations take more effort and practice than you might want to exert, even if you went to school before calculators became available. If you're interested in packing a few of the tables around, make sure you practice a bit, as it's very easy to make mistakes. Your best defense against errors is to religiously practice order of magnitude estimation of the answer (this is still excellent advice even if you use a calculator).

2. ### jpanhalt Expert

Jan 18, 2008
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My pharmacology professor had us learn how to do dosing, volumes of distribution, half-lives, etc. knowing that the log of 2 was about 0.3 and the log of 3 was about 0.5. It was close enough for government work.

I agree that hand-held calculators are a lot easier, but I become a little dismayed when I ask a student that if 10 mmoles weigh 2.5 g, how much do 20 mmoles weigh, and they reflexively reach for their HP graphing calculator.

John

3. ### steveb Senior Member

Jul 3, 2008
2,432
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You've inspired me. I'm going to make business cards that have log scales on them. I'll just always give out two of them, and everyone will have a usable slide rule accurate to 2 or 3 significant digits.

Just kidding, but your idea is pretty cool. I'm curious if the youngsters will appreciate it.

4. ### RiJoRI Well-Known Member

Aug 15, 2007
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Be lazy -- print the tables on log graph paper!

I remember seeing a 6" plastic slide rule the fit nicely into any geek's -- errr, engineer's -- shirt pocket.

--Rich
P.S. -- I like the idea of the mini-tables!

5. ### someonesdad Thread Starter Senior Member

Jul 7, 2009
1,577
142
About a decade ago I wrote myself a little graphical language and a few years ago used it to produce a page with slide rule type scales on front and back. It was, in some sense, a nomograph analog of these little tables. It worked pretty well and you could do slide rule type calculations if you had a pair of dividers handy (which of course no one ever does except perhaps on the bridge of a ship). But these little tables are handier, as they fit into a much smaller space.

In the early 80's, I really liked the little circular slide rules made by Concise (imported by Sama and Etani on the east coast) that came with the built-in conversion tables, etc. They easily slipped into a shirt pocket and were quite rugged -- and they gave quick answers when you were away from your desk, calculator, and computer. But they're kinda hard on over-40 eyes...

6. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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I like the idea, but think it can be expanded.

They have "Swiss Army Credit Cards", which have all sorts of tools that slide in and out.

Why not a Log-Log Slide rule built into slightly thicker credit card package, and then the common conversions and formulas printed on the back, such as linked in the above PDF, just not the tables.

That would give the best of both worlds! With the printing and injection molding technology we have today, I don't think it would be any great feat to mass produce them for under \$1 each, and I know I would buy one!

7. ### someonesdad Thread Starter Senior Member

Jul 7, 2009
1,577
142
As I mentioned above, something like this was being made and imported into the US about 30 years ago (you can still find them on ebay and I still have one or two somewhere around the house). Frankly, these little tables are substantially more compact than these slide rules were and something you can print yourself cheaply. To make good plastic slide rules like the ones Concise made (BTW, you can still buy them today in Japan), there's a significant investment in tooling, as you want the printing to be recessed so it doesn't rub off. I also have a few circular calculators made by both Mears and Fearns in the UK and they're made the same way -- but they get \$100-\$200 for each of their calculators. I bought these 30 years ago; they are industrial strength and will easily outlast me.

Oh, another nail in the coffin for the small slide rules is that the geezers can't easily read them. But I made these little tables so that they print in a condensed Helvetica bold font that I don't have to use my glasses to read, at least in good light.