Armpits are not Metric
- or -
Reflections on various issues surrounding roll-on antiperspirant / deodorant applicators
First Issue 12/10/2001
Introduction
I was sure this would be of great interest to everyone, so decided to share my thoughts with you on a topic that - perhaps - does not always occupy your mind during every waking hour. In a nutshell, we are going to be thinking about several facets of the dispensing marvel which is the common-or-garden roll-on antiperspirant / deodorant (hereafter referred to as r-a-d for brevity), and in particular the business end which is the ball.
The Collection
Let me introduce you to these delightful things without further ado. They are part of my r-a-d ball collection. As a pastime, you could do a lot worse than start your own collection - the activity is not overly-physical, and might be particularly suitable for someone who pursues a lifestyle of chronic laziness - mostly long periods of nothing much to do, with occasional bursts of frenzied activity when a bottle suddenly becomes empty.
The Thoughts
The first thing you might notice is the apparent equatorial marking present to a greater or lesser extent on each of the balls in the photo. That's because they are all made of PLASTIC. Horror of horrors. I remember the days (long before I started collecting) when they were made of glass. Nowadays, they seem to be moulded from two hollow plastic hemispheres fused together with remarkable precision.
The principle of operation is unchanged from the earliest days of r-a-ds - basically a ball point pen for armpits, but with transparent ink. The surface texture of the ball is microscopically rough, in order to retain a film of the vital fluid which facilitates the majestic triumph of chemicals over body odour. Presumably the plastic fabrication has commercial advantages in terms of manufacturing cost and shipping weight. In armpit terms, it feels warmer on the skin than glass, reducing one of the ** ouch ** factors when first encountered on a cold Winter's morning.
As a delivery system, the r-a-d seems to me to be almost ideal for its intended purpose - a few key points which spring immediately to mind are: no volatile propellant, no pressurised container, well-controlled delivery to target, contolled delivery volume (indeed, self-regulating, in as much as the ball slips and stops rotating on a well-saturated armpit), highly portable, silent, low respiratory impact and so on. As to the overall manufacturing energy and non-renewable resources cost and environmenal impact of this method of application compared to others, only a serious analysis by the various manufacturers would give us the true picture - such analysis would need to take into account the cost of obtaining metals, chemicals, plastics, transport, handling etc etc. From a practical point of view, the only drawback I've found to r-a-ds is that if you put one upside down in your luggage on a plane, the reduced air pressure at altitude tends to cause it to leak big-style all over anything in the vicinity - BlankFrank's hot tip for air travellers is to make sure your r-a-d is stored upright in your carry-on baggage, preferably double-wrapped in paper towels and polythene bags.
Another thing of note, though not obvious from the photo, is that the balls illustrated are all almost perfectly spherical, with a mean diameter of 1000 thousandths of an inch (the entire range is only +/- 0.002 inch, as far as I could determine with my micrometer). This is something I find astounding. Exactly 1 inch diameter. Ideal for measuring things when you find yourself caught in a measuring situation and you don't have your measuring tape with you. The suggestion is that the mechanism was invented in the UK or the US, and that armpit geometry is measured in Imperial rather than Metric units. Bizarre, when you consider that the size of an armpit is controlled by skilful (I'm reluctant to say dextrous) but arbitrary adjustment of the upper arm / torso angle, and can be made to conform to objects of a range of sizes covering at least -50% +100% of nominal. To put it in perspective, the complete variation in size from the smallest to the largest of the examples shown is approximately the same as the thickness of one sheet of 80gsm photocopier paper. Is this one of the few remaining areas of science where SI units have not been adopted, or where the EU has not stuck its bureaucratic oar in? Oops, sorry, nearly got political there.
Clearly, there are many factors to be weighed up when designing a r-a-d applicator. Here are a few.
- Maximise consumption of solution, to increase sales frequency
- Minimise consumption of solution, to make customers appreciate economy of use and come back for more
- Minimise transport costs - keep it as light and small as possible
- Maximise capacity for a given size, to keep customers happy
- Minimise use of construction material - hollow balls, as thin-walled as practically possible
- Optimise ball size to suit the majority of armpits
- Minimise the effects of manufacturing tolerances - keep ball housing as elastically compliant as possible to absorb manufacturing variation, while retaining ball, keeping friction low and keeping the production assembly process simple and physically easy
- Optimise ball surface roughness for best delivery efficiency, for given viscosity
- Optimise viscosity for chosen delivery system
Conclusions and ideas for further reasearch
Armpits are Imperial, not Metric. A bold conclusion, I concede, but on the basis of the physical evidence in my possession, hard to refute.
The r-a-d is something that most of us take for granted. We accept it without question, which I personally find, on the one hand, to be evidence that the idea is pretty much perfectly developed, and, on the other hand, quite sad because there seems to be a lot more to the subject that people simply fail to think about it. I hope this page will provide food for thought, and will perhaps inspire readers to take a closer and longer look at commonplace items - just because it doesn't have batteries or a micro doesn't mean that it isn't clever, and I think it's high time that people appreciated it for what it is.
As to the matter of further research, my collection and measurements are based on a limited number of examples of the art - it would be interesting to hear what other people in other parts of the world, or other shelves of the toiletries department of the supermarket, can find out about r-a-d ball diameter. Given enough statistical data, it might be possible to establish that our historical system of linear measurement is actually based on optimal armpit-applicator dimensions rather than platinum rods, wavelengths of light, emperors' noses, thumbs, coins, etc. Then again, maybe not. Whatever. You pays your money, you gets your roll-on antiperspirant / deodorant.
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