You may have never heard of, or thought about such a notion as "The Threshold of perception". In fact, for thousands of years this idea would have been inaccessible to all but a few people. In order to grasp the threshold, one must see it move!
 
There are things that are too small for the human eye to see, but they exist. When one has seen a magnifying glass 'push back' the threshold, the principle is established. It is then easy to imagine that increases in magnification will reveal still more unseen things.
 
Vision, like all of the senses, is  constrained in many dimensions. There are things that are too small, too large, too distant, too close, too slow and too fast to see. There are colors of perception that we can directly experience only with the aid of technology.
 
Fortunately, direct experience is not the only tool at our disposal. Think, for example, of a Sherlock Holmes who can deduce the likely height and weight of an unseen individual from the stride and depth of footprints.
 
In business, even our engineers sometimes forget about the threshold and act contrary to good statistical evidence because they "don't hear or see anything."
 
One client was "bubble packing" its small product, and about 1% of the finished goods were scrap. The company was profitable with scrap rates below 2%, but an aggressive manager wanted to know why his machines would occasionally fail.
 
A time series study showed that at particular points in time there were slight variances in finished product weight. These variations were negligible with regard to the product's performance, but they signaled the presence of causes and their effects that were below the threshold of perception.
 
We correlated the variances to a sloppy overuse of a powder lubricant, and the plant engineers laughed. "Momentum!", they said. "Do you seriously believe that a little of this light powder can have the slightest impact on this heavy stainless steel conveyor and the heavy duty electric motor that pulls it."
 
"Just look", they said. "The conveyor is sweeping away the tiny amounts of excess powder!"
 
Nevertheless, operations took our advice to heart and eliminated -all- of the scrap with two new additions to their knowledge of a "correct process." One of those was a change in the way the powder reservoir was filled. The gallon-sized powder scoop was replaced with a one quart size. With tools that were commensurate to the manual task of scooping powder and adding it to a machine reservoir, excess powder was eliminated, and so was scrap.
 
The exciting (and relevant) rest of the story is what happened next. A gadget salesman made a call on the plant. He offered a camera technology similar to that used in Disney's nature photography, and he demonstrated his product on a packing machine conveyor.
 
Time was slowed by a factor of ten, and the effect of excess powder on the conveyor was finally seen. Each conveyor cup jerked and rocked over the granules of powder like a car on a rocky road. Each transient event was faster than the eye could see, and human vision was integrating these small variations into an average of continuous motion.
 
The cause (powder) was not without effect in the packaging process. Each small bump increased the variation of package position when the package sealer fired. The excess powder materially increased the likelihood of a "registration" (position) error when the product was packaged, and was the ultimate cause of a substantial quantity of scrapped product.
 
Sometimes the limitations of perception is not in the nature of our eyes and ears, but in our willingness to use them.
 
A client was experiencing a small percentage of defects in its rubber glove manufacture. Hundreds of forms were pulled by conveyor through a hundred yards of machinery where they were washed, dipped in latex, and then heated in a gas-fired oven.
 
Since the BTU (heat capacity) of natural gas can vary, operators knew that they had to monitor the gas flows and occasionally adjust them to maintain a target temperature. "What does the gauge say?", I asked the operator.
 
"180", he said, knowing what the answer was -supposed- to be. He looked again. "160? 150?" He peered at the gauge through thick glasses.
 
Although there was plenty of cable,  maintenance had placed the temperature gauge at a height of 7 1/2 feet - well over the operators head. Perhaps the last operator had been very tall!  This was not a failure of the near-sighted operator, but of the company. They did not value and facilitate attention to details. (In this example, the potential of automation is beside the point.)
 
The company's attitude to details and housekeeping was confirmed as I walked the long aisles between the machines. "What is this?", I asked.
 
"Why, it's just a small puddle of water. It's no big deal. Every one of these machines has a "washing" station where the latex forms are cleaned. Surely you can't blame a puddle of water in the aisle for scrap product! I just can't see any connection."
 
"We are looking for evidence of things that you -can't- always see.", I said. "If the water is here, where is it supposed to be? What is behind that door?"
 
The door was an access panel to the "washing" station. It had not been opened in a while, and we moved it with difficulty. When we looked inside, a spray-washer was misaligned - pointed at the cabinet housing and not at the latex forms.
 
Because they forget about the unseen world beneath the threshold of perception, operators don't always grasp the importance of housekeeping and attention to small details.
 
For example, one operator may neglect to use required gloves or wash their hands before handling a product. Or, they may imagine a "technician's prerogative" and rearrange or even leave out steps in a critical process because, "they can't see any difference."
 
In order to progress past a certain point, business must educate their associates that a world exists outside their threshold of perception. Sometimes that world of small details is revealed simply by opening a door.