Is it me, or is the inch the problem?

An issue with units and scale

Approx. 1000 words; five minutes read time

This last week while working in my shop, I had a “brain glitch” of sorts - a quarter-inch looked twice as big as it was. While this might not sound like a big deal, it was significant for what I was making. I almost drilled two holes off by a quarter inch - in a project only 12 inches wide. I've spent a week building it, and the miss-drill would have been a big screw up.

Thankfully, I always measure twice. Well, almost always. I did this time and caught my mistake; the error was evident on a second look. But it left me thinking, what was going on with my eyes? My brain? Or was the problem something else external to me?

---

Now that I am making (and writing) fulltime, I spend a lot of time staring at minutia. It's not uncommon for me to belabor over 1/64th inches - that's just 15 thousandths (0.015) of an inch. Smaller still, I aim for less than five thousandths (0.005) inch tolerances in my cutting and drilling. That's the width of a human hair. 

While these measurements sound too small even to see, they aren't. People can discern a lot smaller.

---

Humans have an uncanny ability to see small things. The average person can make out objects as little as 15 ten-thousandths (0.0015) of an inch (with good or corrected vision). The challenge is seeing the difference in sizes. Here, humans have varying degrees of perception. 

While some people have a "good eye" for tiny differences, others seem oblivious. But whether this is an actual distinction in people's abilities or a matter of learned discernment is not clear.

---

I experienced an informal test of this the other day. I had a piece of acetal plastic that was just about six inches long. And it was one inch wide, and one inch tall - the whole thing was about the size of a hotdog (if said "frank" was square in cross-section, that is). The piece was uniform, aside from one tiny difference. 

Looking at the plastic, I could see that it varied over its length; one end was ever-so smaller than the other. Curious, I broke out my dial calipers to examine it further. Measurement confirmed my suspicion - one end was narrower by 0.004 inches (again, that's about as wide as a hair). Over its six-inch length, that's less than seven ten-thousandths of an inch difference per inch (0.0007 inches).

My curiosity was now piqued. Had I lucked out, or did I really see the variation? To experiment further, I closed my eyes, tossed the plastic on my workbench, letting it bounce around. Opening my eyes, I tried to pick the smaller end again. Each time I could identify it out without fail. 

I really could see the difference. 

Now for the big question - did I have some unique ability to see small differences? Or was it something most people could do if they paid attention? My "good eye" is why I am proficient at making, right? I must be special, I hoped.

This needed verification - the scientist in me had to know for sure.

---

Taking my experiment to the next level, I took the plastic to show my son and his mom. Surely they couldn't tell the difference as I could. 

To my amazement, my son picked out the smaller end right away. His mom got it wrong - but only on the first try. I remained optimistic - it was genetic, and my boy inherited his excellent eye from me!

Not so fast.

She had been thinking about something else and didn't pay attention - at first. But after she focused, she too could easily see it. And no matter how many times I had them look away while I flipped it around, they could both pick the smaller end. Every time.

It would seem that many of us can notice these tiny differences, so long as we pay attention. 

---

Back to my measurement problem.

I believe my eyes are fine, as too is my brain. What is happening has to do with the size of things I am often observing. Because I am so focused on small sizes right now, they seem familiar, in a way. They’re more roomy, so to speak, with more space for other subdivisions.

In my "big" life of driving, riding my bike, and walking around the house and lab, a quarter inch is nothing. But in making, it is colossal. I've become so used to thinking smaller that my ruler's measurements seem bigger.

---

I'm reassured - I can see and measure fine. But I must focus to do it right. Almost always, I have to take a double-take in reading my ruler - is that a half-inch? A quarter? An eighth? Or is it a sixteenth or thirty-second? And why oh why are these things not more systematic?

All this focus on tiny measurements leaves me squinting at times. Trying to keep those fractional sizes straight is tiresome. But I'm sure it's not only me. Instead, it might very well be the system I am using. 

Who came up with this measurement scheme anyway? Whether you call it Imperial, SAE, or even the "American way,” there's nothing "standard" about it. 

It looks like there could be something more manageable. 

Here's an idea: maybe take a length, divide it up by tens, and then take those lengths, and divide them in tens. Up and down in size, all by tens. You could go as small or as large as you want, but all divisions would be by ten.

Innovative. Simple.

Let me know if you learn of anything so revolutionary. Meanwhile, I'll be fussing over inches in my shop.

---

Until next time. Science. Fiction. Create.