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          Biorhythmic calculators

Where computing meets Pseudoscience

    Slide rules are usually considered in the context of scientific instruments, but there is at least one group of them that is made to support pseudoscience. These are the Biorhythm calculators.
The Bio-Slide Biorhythmic Slide Rule
Bio-Slide Biorhythmic Slide Rule (back)
Click a photo to enlarge
    The solidly debunked Biorhythm theory posited three temporal cycles of different lengths governing people’s lives: a Physical cycle of 23 days, an Emotional cycle of 28 days and an Intellectual cycle of 33 days, which all start off together at the moment of birth and continue with total precision until death. Biorhythm curves
Click photo to enlarge
The idea was that as these cycles waxed and waned, the individual’s likelihood of faring well or otherwise in each domain was affected; and when a cycle crossed the zero line, one had better beware! Those “critical days” were prone to accidents and mishaps.
    Bogus or not, many people in the 20th century believed the theory, and they needed a way to figure how their three rhythms changed from day to day. The math is trivial; you need to compute three sinusoidal functions of your age in days... but then, one can conjecture that people capable of trigonometry would be unlikely to put faith in biorhythm in the first place. So for those who did have faith, various tools were produced. Late in the century these were simple computer programs, and such are still available today; but before the PC made computing ubiquitous, people used mechanical sliderule-like devices for this function. I have three different types in my collection, and they have a strange beauty all their own.
    Each calculator uses a different configuration to do so, but all have the same elements to allow checking one’s rhythm state: three scales marked with the three cycles and a scale for the days of the year, a system to set these up in the right relationship to each other in accordance with the user’s birth date (using tables provided on the back of the instrument), and a cursor that when set to a given date shows the values of the three cycles on their respective scales.
    The Bio-Slide Biorhythmic Slide Rule seen above is the simplest in concept. Its instruction sheet originally stated its source as International Marketing Services of Santa Monica, CA, but this was crossed out and a sticker updates it to C.E.I., Inc., also in California. It has three transparent sliding scales showing the three curves for the whole year, and a fixed frame bearing the dates. Once you fix the scales to represent your personal starting point, you can use the sliding cursor to see how your cycles line up for any date in the year.
    The Biomate, which is made in Japan, is more sophisticated. It uses non-concentric circular scales geared to rotate at the required different rates when you turn the wheel at its bottom edge; this makes for a compact and durable instrument. Setting the initial configuration is done by pulling the wheel downward a bit to disengage the gearing, allowing the cycle and date wheels to be rotated freely to the desired relationship. This calculator does not show the full sinusoidal curve for the year; its wheels show only 2 or 3 sine cycles that repeat when they turn.
Biomate Biorhythmic slide rule  Biomate Biorhythmic Slide Rule (back)
Click a photo to enlarge
    The third calculator I have comes to me from Bulgaria, but for all I know may originate in any other country where Cyrillic script is used. It too is circular, but unlike the Biomate its scales are stationary once set in the right relationship, and the cursor is rotated to intersect them. In actual use it seems far less convenient and harder to read with precision.
East European Biorhythmic Slide Rule  East European Biorhythmic Slide Rule (back)
Click a photo to enlarge
    The packaging of the two western calculators is surprisingly ornate. The Bio-Slide came in a large cardboard box with leather-like finish on the outside and yellow silk lining on the inside; the Biomate in a fancy blue silk pouch. The Bulgarian unit comes in a more frugal but very functional plastic box. And all three come with instruction sheets (see links below).
Exhibit provenance:
    I found the Bio-Slide in a computerfest sale in California. The other two devices come from two different eBay sellers.

More info:
    You can download here scans of the instruction sheets for the Bio-Slide and Biomate.

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