Phono stylus rake and (cantilever) vertical tracking angles

frequency response

Sampling shorter sections of record grooves will recover more high frequency information.
Sections sampled are shorter by elliptical AKA biradial than conical AKA spherical styli.
To reduce wear and pressure, micro-ridge styli elongate contact area along an axis nearly normal to disc plane and groove direction.
The nearly arises because records are cut with on average 92 (rather than 90) degree stylus rake angle.
To maintain effectively shortest sampling sections, micro-ridge styli should be aligned to match record lathe cutters.

alignment

Practically, few audiophiles have access to equipment for precisely measuring so-called rake angle of a micro-ridge stylus.
Some users may measure stylus shank angle and suppose that working stylus shapes are ground with ridges parallel to shanks,
despite no known (to me) documentation from manufacturers explicitly supporting that supposition.
However, (cantilever) vertical tracking angles are commonly specified and relatively easy to measure.
In theory, styli can be aligned by adjusting for strongest signal response to high frequency groove modulations.
Using a personal computer, free software and audio interface,
many users could also in theory make such high frequency response measurements.

Practically, many turntables lack convenient adjustments for vertical tracking angles.
Consequently, optically measuring vertical tracking angle before attempting tweaking based on audio signals
is likely to expedite approaching optimal alignment. While this depends on manufactures mounting styli
with rake angle correctly fixed relative to specified cantilever angle, it is at least a good place to start
any subsequent tweaks based on LP playback.

Analog Planet and USB microscopes

Michael Fremer's article motivated measuring stylus rake angle.
Instead of his $249 Dino-Lite, I used a $25 generic USB microscope.

This device was plug and play on macOS High Sierra and works on Windows 10 with an automatically installed Microsoft device driver,

but I had to disable the camera built into a monitor before Microsoft's free Camera app would use the USB microscope.

While Mr. Fremer invested in a better desk stand, I steadied the USB microscope near the stylus by resting it on an Pink Pearl eraser.

Instead of using the microscope's built-in light, back-lighting a folded paper resting on the record behind the tonearm gave better results.
To minimize distortion of angles in video, aim the microscope square to the side of the cartridge and parallel to the record surface,

Instead of trying to capture a still image in focus, I recorded video while slowly moving the camera thru focus a few times,

then stepped thru video playback to an in-focus frame and captured a still by [Ctrl]+[Print Screen]

and pasted that into Irfanview, which is free and handy for this purpose because of an option to precisely rotate images.

Dragging a mouse cursor over an image in Irfanview generates a box for cropping
and/or for vertical and horizontal references to features in those images.

A first rotation makes the record surface horizontal.
Crop and save that image, then use it to measure stylus and cantilever angles.

With AT-LP140ZP tonearm base cranked all the way down, cantilever angle measured about 26.5 for a record on a 2.5mm platter mat.
7mm total mat thickness yielded 21 degree VTA, so 4.5mm mat (or tonearm height) change corresponds to 5.5 degree change.

A-T VM95ML microline is visibly uncentered in stylus shank; only A-T knows whether their microlines are ground exactly parallel to shanks..
Meanwhile, A-T specifies a (23 degree) cantilever vertical tracking angle, which is easier to measure and set as a starting point for any subsequent audio evaluation.