Diagonal wobble is a regular displacement of the tablet's interpretation of the pen's position.
You might also see this referred to as: "jitter"
I covered wobble extensively in this video on pen display accuracy (https://youtu.be/M4rEk_RNBrM)
If you slowly draw line on a tablet WITH A RULER the wobble will be apparent on diagonal lines. The diagram below exaggerates the wobble
The wobble can happen with any kind of pen movement - straight lines, or curves.
As the name suggest, the wobble is apparent with the pen is moving at an angle.
A 45 deg angle exhibits the most wobble
A 0 deg or 90 deg angle exhibits no wobble.
Angles between 0 and 90 exhibit more wobble as they approach 45 degrees.
The wobble is just more obvious with straight lines even the the same amount of wobble occurs with curves
Generally the wobble will be present the slower the pen is travelling
Some tablets exhibit the wobble even when moving the pen fast. This is less common.
Diagonal wobble is present in all drawing tablets in varying amounts.
There's no clear pattern by price or by brand or by device type about when wobble appears.
The wobble is NOT due to the nib wobbling in the pen.
The nib can be perfectly fixed in the pen and you would still observe the wobble.
In any case, remember that the nib is not what the tablet senses to detect position, but rather the inductor coil deeper inside the pen.
The wobble comes from the tablet and how it senses the pen position.
The wobble is due to how the tablet senses and interpolates the pens position.
The wobble is present in multiple digital pen technologies
The wobble is present with EMR pens
The wobble is present with non-EMR pen technologies such as MPP, AES, and the Apple pencil.
If there is wobble, it tends to show up at slow speeds. This is a bit expected.
If the wobble shows up at faster speeds, that is unusual.
Tilt could affect the wobble.
Most often I have not seen tilt have an affect on wobble, but I have tablet where an extreme tilt angle (an angle that would not be used in drawing) causes a massive wobble. I haven't tested all my tablets at extreme tilt, so I am not sure how common this is.
All tablets have wobble.
But for most, you would only notice the wobble when TRYING to find the wobble. In other words, it won't affect your normal drawing.
The real problem comes when the you notice the wobble creating alterations to the strokes that you didn't intend.
It also depends on what you are doing. You might notice wobble more if you are doing line art but not notice it at all if you are using an airbrush.
OPTION 1 : Turn on smoothing
Applications have different brush smoothing options. Explore those to see if they eliminate or reduce the wobble.
OPTION 2 : Zoom in
Try zooming in on the canvas in (for example by 2X) and drawing the same stroke. The wobble will technically still be there but because it is a happening on the physical moment of the pen, if you zoom 2X with the canvas in it will have 1/2 the effect on the stroke.
OPTION 3 : Draw a faster
Wobble is often something that occurs when you are drawing slower. Try drawing the stroke faster, in most tablets this eliminates the wobble.
If your strokes are small and drawing faster would cause you to have less control, then try zooming in more. This will make your physical stroke longer, but keep them the same size on the canvas.
OPTION 3: Use vector tools and brushes
Instead of drawing your stroke manually, if your application supports it, use vector strokes.
These are my wobble samples across a number of tablets.
https://1drv.ms/f/s!Aml8i4Jd6crChTjTXo89k5jO8mb8?e=t3ijPC
All were created using my a standard testing process: Diagonal wobble testing.
Some recent models with XP-Pen feature some excessive diagonal wobble. This is something you should check into when looking into these models. Here are examples of of the line wobble in recent XP-Pen:
XP Pen Deco LW 8:06 in this video : https://youtu.be/0VaH-UTRL7A?t=486
XP Pen Artist 16 (GEN2) 7:04 in this video: https://youtu.be/0VaH-UTRL7A?t=486
XP Pen Artist 12 (GEN2) 5:45 in this video: https://youtu.be/O6OzBT7BLsA?t=345