Sorry about that... I was responding to the original poster of a thread you apparently bumped from the past (regarding cast table extensions), and didn't pay enough attention to the details in your post, which I thought was in response to the OP, not a new case.
regarding the Bosch 12" Glide Saw.
Yes, an inattentive human arm can impose a lateral lean to the saw's glide arm at the farthest reach of travel, by pulling to the left or right, or by not being cognizant of the human arm's lateral arc of motion that is a natural result of a horizontal grip and an outward extending elbow... not tucking one's arm in when operating the saw.
Some characterize this as a flaw of the saw. I find it to be a feature of the saw, and any flaw in not discovering this feature, to be either used or avoided, rests with the operator.
Very little in home construction or remodeling is perfectly square, level, plumb, beveled or mitered. When cutting angles to match existing work in a remodel, or the quick, fast, and consequently sloppy work of other trades in new construction, I often find that I need to cheat angles a little in order to obtain tight or gapless fit ups in corners. So 45 degrees becomes 45+ or 45-, to compensate for bowed walls, bulged rock, or botched buildings.
I think most people who saw wood do this, even with straight cross cuts. Inside the line, outside the line, on the line, half on, half off the line... these are decisions we sometimes make "on the fly" depending on what we previously found was too long or too shy. Adding the element of angle deviation is like having another tool in the box.
So how much deviation can be manually (and quite cognizantly) "forced" on the Bosch Glide Arm's excursion over the full length of it's cross cut travel capacity? Keep in mind, I own this saw, and have cut a lot of wood with it. I didn't just play with it for a few minutes at a store, or read reviews about it. The opinions and observations I'm sharing here are my own, developed with several years of experience with this saw. The photos, and the ideas for the photos, are mine as well.
The lock knob area at the end of the trough represents a distance greater than the glide arm can travel, and thus any cumulative deviation measured there would represent the maximum possible deviation from the origination of travel. The perfect vector is indicated by the first photo below, where the laser line is dead center in the trough, equidistant between the left (purple) and right (green) arrows:
Now, if I shove the glide arm toward the left while I'm gliding the saw head toward me, I can force this much deviation left:
Consciously forced left bias.
Likewise, if I shove the glide arm toward the right while I'm gliding the saw head toward me, I can force this much deviation right:
Consciously forced right bias.
With mere conscious awareness of the influence that my arm can impose on the saw's arm, the saw can cut PRECISELY where I want it to... left, right, or center.
Consciously RELAXED, with a mindful, neutral human arm operation, purposely aiming to have the laser land on the line separating the different colored arrows.
The glide arm suspends the weight of the saw, and guides the arm straight. Humans who operate the saw may not be aware of the influence of their own arm motion.
Try this experiment. Reach your hand out above your head, palm facing forward, hand high, as if you were palming a basket ball in the middle of a slam dunk, or as if reaching for the top ledge of a cliff you are trying to climb up. Physically do this reaching now... don't just imagine it in your mind... otherwise the point will be lost.
Now, clench your fingers as if grasping a hold of the horizontally oriented handle of a miter saw, and go ahead and pull your arm down. Reach up and pull down several times. How vertical is your hand traveling? Line your body up to a vertical line on the wall, such as a door frame, and do the exercise again. If you are right handed, and operate miter saws with your right hand, be sure and reach up with your right hand. Do you not notice how as you pull your hand down from up above you, that it not only goes down, but also goes toward the right?
Furthermore, the further away you elbow is from your body, the more horizontal drift can be observed in the hand from it's highest reach, toward its downward travel termination at waist level. This is critical to be aware of.
Another exercise: Now hold an imaginary gun in you hand. Raise your hand high, as if holding a starting pistol. Now, keeping the gun pointed toward the front at all times, lower your hand to waist level. It does not matter whether you keep your arm straight, or bend your elbow. The only thing that matters as you lower your arm is keeping the gun pointed toward the front.
Observe your wrist as you lower your arm. Holding the gun forces the wrist into a VERTICAL grip, as opposed to the more wrist friendly, ladder climbing like HORIZONTAL grip, as the previous exercise modeled. With the gun in vertical grip, notice how, as you lower the pistol from above your head in the starting position, the arm and wrist tend to travel in much straighter vertical line as you keep the gun pointed toward the front.
Another visualization is pulling the chain on a shop light, or climbing a rope. The arm tends to move up and down more perpendicularly with the wrist oriented vertically. Note than the Festool KAPEX miter saw, vaunted for it's accuracy, also has a vertically oriented grip. This jail house bar grip is not favored by many, as it is not as comfortable to reach up for and pull down as is a horizontal grip. like a ladder rung.
And therein lies the problem... some saw operators might carry over comfort with their grip orientation of choice to comfort with how they bring their arm down in saw operation. The human arm movement that enables the highest precision is not natural. It is uncomfortable. It is not mindless. It is quite mindful. And with a horizontally oriented grip and a wide elbow that bio-mechanically forces the right hand to drift sideways as it lowers anyway, even more thought must be applied to the downward motion when operating a miter saw with a floating glide arm.