A few blogs back I noted one man’s quest to expand his knowledge by reading the entire Encyclopaedia Britannica. It’s nice to learn the facts. Sometimes, though, we don’t have that luxury. We just don’t have all the relevant information about something in front of us, and neither the Britannica nor our latest generation iPhone can provide it for us – at least not in the requisite time window. We nonetheless have to make our decisions based on our sketchy data. On those occasions we rely on Rules of Thumb.
The phrase “rule of thumb” has existed for centuries in several languages, and apparently derives from the use of thumb width for rough-and-ready small measurements. Thumb also means “inch” in several languages including Dutch (duim) and Sanskrit (angulam). Using your thumb in this way is inaccurate, but, for many applications, good enough. That is the whole point of thumb rules: it is better to be approximately right than to be wrong with a high degree of precision. Rules of Thumb are not facts, they are not laws, and they are not 100% reliable, but most of the time they will get us where we want to go, more or less. Sometimes that’s the best we can do.
Some years ago, Tom Parker set out to collect a bookful of Rules of Thumb. Calling himself the Alpine Planetarium (which he hoped would sound serious enough to stir responses), he sent out inquiries to people in all walks of life from economics professors to gravediggers. He published the results in a book titled, unsurprisingly, Rules of Thumb.
The list is oddly intriguing, even though I’ll never have any use for the bulk of them. It’s at least possible some might come in handy, for example, #797 “seven quail eggs equal one chicken egg” and #798 “one ostrich egg will serve 24 people.” I’ve never cooked any eggs other than chicken, but I suppose it could happen. Some of them are esoteric, e.g. ”a Learjet 25g will float about an extra 100 feet down the runway for each knot over its proper landing speed” and “inviting more than 25% of the guests for a university dinner party from the economics department ruins the conversation.”
103. PLAYING POKER. Don’t enter a poker game unless you have 60 times the betting limit in your pocket. When you have doubled this amount, quit.
314. USING DYNAMITE. Wait at least an hour before investigating a charge of dynamite that didn’t go off.
[I might wait two.]
322. BUILDING WALLS OF ADOBE. The height of an adobe wall should be less than ten times its thickness unless reinforced with buttresses.
357. USING A HOT TUB. Soaking in a hot tub adds two to three pints of perspiration per person per hour to the water.
386. TAKING A FEDERAL EXAM. On any government multiple-choice test, the longest answer is usually the correct one.
480. MAKING CRIME PAY. Commit a federal crime rather than a state crime. Federal judges are more worldly and less likely to send you to jail, or for as long. Also, federal prisons are nicer places to stay.
539. THE TRAVELING RULE OF TWO. Take twice the money and half the clothes you think you will need.
544. DEBUGGING AN OFFICE. Checking an office for electronic bugging devices takes at least 4 hours for every 5000 square feet of office space.
682. SHOPLIFTING. One out of every forty to sixty people in a store is a shoplifter.
746. LEADING A SEMINAR. Allow six seconds for a response to your questions. If someone is going to respond, they’ll do it with six seconds.
896. DEALING WITH DOUBT. When in doubt, don’t.
As I’ve grown older I’ve embraced #896 more, though without ever verbalizing it that way. I know I’ve missed golden opportunities thereby, but I’ve also avoided stepping into an abyss or two.
We make most of our decisions by such rules, not least in matters of politics and personal relations. Our rules save us too much time to do without them. I’ve learned the hard way, though, (as yet another rule of thumb) that they do – not might, but do – lead us astray sometimes. Jonathan Swift is, after all, being satirical in Gulliver’s Travels when he is fitted for clothes by a literal rule of thumb: “Then they measured my right Thumb, and desired no more; for by a mathematical Computation, that twice round the Thumb is once around the Wrist, and so on to the Neck and Waist, and by the help of my old Shirt, which I displayed on the Ground before them for a Pattern, they fitted me exactly.”
Uma Thurmon rules with a spectacular thumb in Even Cowgirls Get the Blues