Bohn Contex 10
This advertisement from the early 1960's is an almost comical example of the 'twists' that can be used in advertising to give the impression that a low-cost product can somehow match the capabilities of much more expensive instruments. A great example of this is the statement, "And for looking twice at our Brainchild that claims to do just about everything the big, expensive machines do...and a couple of things they can't." Note the italicized words. Note how the ad writer dodges any commitment by using the word "claims". And the sly inclusion of "just about". The simple fact is that the Contex 10, while a very interesting and unusually-designed all-mechanical calculator, requires a fairly high level of user training to operate, does not perform multiplication or division automatically (straining the definition of calculator), requires paper and pencil to record the results of division operations, and is much slower than motor-driven rotary calculators. The ad goes on to claim that the Contex can somehow match the "automatic decimal indicator" of much more expensive machines. The omitted fact is that the decimal indicator on the Contex is manually operated, not at all automatic. The claim that the more expensive calculators can not "double as a high-speed 10-key adding-subtracting machine" is clever, in that while desktop rotary calculators can easily out-pace the Contex in addition and subtraction...the rotary calculators are not "10-key" machines, using instead full keyboards. Even though some of the claims are more like carefully-worded spins, the Contex 10 was, for it's price, a functional, easily portable, and rugged little machine. The Contex 10, not surprisingly (advertising claims aside) sold well for these reasons.