Indeed I can try. Like every emoji or abbreviation that indicates some form of laughter, (ahem “lol” ahem), nowadays it basically just means that “this-short-sentence-is-not-aggressive-and-here’s-an-emoji-or-abbreviation-to-prove-it.”
In this case it means I’m not preaching or being too serious.
But I always hate it when someone gives in a thumb-up in a text message (on the phone). It always feels like “whatever” to me. Even though I know it most often just means “got it” or “understood”.
Now this takes the discussion into the direction I hoped for. The one definition I considered was the orthogonal distance between pedal mounting points divided by axle width. The problem with it is that it is 1 at zero Q, not zero.
Now that I see your idea I would suggest another alternative that can be calculated solely from the unicycles geometry without relying on the physiology of the rider:
Q_3 = (w_p - w_a)/w_a
where
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w_p is the distance between the pedal mounting points measured orthogonally to the cranks.
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w_a is axle width (the full width, not between bearings.)
The downside of this definition: The numbers tend to be quite close to zero. But zero Q is zero Q.
Even worse, it takes two easy to understand and work with numbers, and turns them into a useless one…
I’d work the opposite side of the problem and just call it: “Pedal offset” (for the definition that only involves the crank) or “tread”/“pedal spacing” (for the total distance).
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Q_3 = 0 means that w_p = w_a, but that’s not the same as saying that you don’t need to widen your stance when sitting on the unicycle. Take, say, a mega axle with w_p = w_a = 50 cm.
I think a simpler, rider-independent, but still meaningful quantity would be
S = Q / h
(“stance factor”?) where Q is the usual Q-factor, i.e. distance between pedals, and h is the vertical distance between axle and seat. Then S would never be zero, but it would give a meaningful measure of how much a rider with seat height h would have to “quack” when sitting on the bike.
Thread spacing means something different, but I like “pedal offset” and “pedal spacing”.
Since the thing called Q-factor came from bikes I’d suggest that the bike definition be used. Even if the Q-factor is not really a factor but a distance.
Q factor is the overall width of an installed crankset, measured parallel to the bottom bracket shell from the outside of one pedal insertion point to the other. You can think of it like this: the larger the Q factor, the farther apart your feet will be.
The Q-factor is effected by the axle length and crank offset (sometimes probably incorrectly called the crank Q-factor).
THIS. Sure, this thread was reaching its typical height of unicycling nerdliness (actually much higher, with actual math involved), but how about something useful that people can understand and work with? How about this:
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Pedal Offset: The measurement defined normally by “Q-factor”, laterally from the thread opening on one crank to the other. The total distance that separates your feet, width-wise. We don’t measure from the center of the pedal because pedals come in different widths, as do feet.
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Crank Offset: The amount of outward “flare” of a crank arm. A “zero-Q” crank would have no offset, but the vast majority of bicycle cranks have an offset of several mm.
Pedal Offset presents the complete picture for a given complete unicycle or bike, including hub width, bearing spacing and everything else in there. This is useful for a specific cycle, or to compare with the Pedal Offset of another cycle. Crank Offset gives just the number for the cranks, which stays the same wherever they are installed. Double the Crank Offset to get the total amount of “flare”.
No more duck discrimination! Ducks are supposed to walk like ducks; they are built primarily for the water, and walking on land is only secondary, so cut them a break! 
Now for the hard part: How to accurately measure your Pedal Offset? It’s not that easy… 
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Through the center of the hub, with crank offset added to the total width of the hub.
Or turn one of the cranks 180deg so it aligns with the other and just measure it directly from one face to the other.
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This is still not fully rider independant as the seat hight depends on the rider.
As always when I try to come up with overly complicated solutions to nonexistent problems someone eventually finds a very sensible and boringly easy approach. 
Obviously. But you won’t be able to come up with a measure of “quack” which is both useful and completely rider independent. If a 12" uni has the same Q-factor as a 36" uni, then the stance of the rider of the 12" uni (most likely a 5-year old) would be much wider–relatively speaking–than that of the 36" rider (most likely an adult). Dividing by h gives you a comparable quantity which says something useful about the stance of the rider. Plus, it only depends on the unicycle itself, not on the natural stance of the rider.
Maybe I’m missing something, but wouldn’t it simply be a measure of the distance between the spindles minus the width of the hub, adjusted so that 0 becomes the “standard” (if there is one)?
This only solves the problem of zero Q not being zero. It doesn’t make it a factor, though. It’s still a distance.
I reckon the Q-factor of a UW comes closest to 0, though there prolly is at about 1-2 cms. The wheel basically is the crank.
Maybe your mathematical background is making your think this has to be somehow related to the mathematical definition of a factor? The word ‘factor’ has more than one meaning:
factor: “a fact or situation that influences the result of something”
From FACTOR | English meaning - Cambridge Dictionary
Given Q is for “quack” (which I have learned from this thread) this meaning was probably the original intent – as Finnspin eludes to above, maybe you’re trying to solve the wrong problem? That is, trying to define something precisely that was never intended to be used that way.
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The issue is that this quantity does not directly tell us how much the rider has to “quack”. The Q-factors on a 12" and a 36" uni could be the same, but the rider of the 12" would most likely have to “quack” much more than the 36" rider, because the 12" rider’s legs are so much shorter than the other.
Like @DrD, I don’t see any reason to insist that the Q-factor is dimensionless (i.e., the ratio of two lengths). But I still think that my Q/h definition says more about the “quack” than the original Q.
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Just consider the 12" being closer to the size of a duck. A duck will certainly quack more when on a 12" where as if it is sitting on 36" it will just relax on the seat or just fly off. No quacking whatsoever 
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Ah, finally someone talking sense!
I consider this problem solved.
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Yes, that would be very close to zero at a UW. On a muni the cranks could be arranged like this to come close to zero 
:
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Looks like a solid plan! Tell me how it rides once you’ve taken it to the trails. 
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