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Carrier Ductronic

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"Hi there,", says the man on TV, "I want to talk to you about ducts." So begins Terry Gilliam's Orwellian satire, the movie "Brazil". An odd movie it is, but the same can be said about the Carrier Ductronic, one of the oddest calculators I've ever seen.

The primary function of this calculator is to assist the design engineer in sizing air conditioning ducts. For instance, the air velocity, corrected for friction, in a circular duct with a diameter of 12 inches and an overall airflow of 500 cubic feet per minute (cfm) can be calculated using the following keystrokes:

   CLR D 12 Q 500 V =

In response, the calculator displays 636 (feet/minute, duct velocity.)

Printed on the back of the calculator is a table of fitting loss coefficients (i.e., coefficients that describe what happens in a duct at an elbow or junction.)

Pressing the CAL button puts the device into regular calculator mode, where it can serve as a basic four-function calculator with square root. It has a few oddities: for instance, it calculates square roots only to three decimal digits of precision. When entering numbers, if you key in more than 8 digits, the calculator exhibits all kinds of strange, buggy behavior.

Had it not been for the fact that just last year, I was working on a software package for a humidification equipment manufacturer, this device would surely have escaped my attention. I wonder: are there many other similar special-purpose calculating devices out there? In the 1960s and before, slide-rule or circular slide-rule type special purpose calculators (made of wood, plastic, or even more often, cardboard) were quite common. Such electronic calculators, however, appear fairly rare.

Of course, the Ductronic's functionality can easily be replicated on most programmable calculators. Nevertheless, it is an interesting piece that I happily added to my collection of oddball calculators.