Don't fret the level, Maestro the frets.
FretMaestro Precision...
like having a CNC Fret Machine in the palm of your hand.
Precision Height:
There are 12 increments of .003" each.
The tallest fret can be .057" and the shortest .024"
The increments are .003" as follows: .057 - .054 - .051 - .048 - .045 - .042 - .039 - .036 - .033 - .030 - .027 - and .024
On the Fret Maestro settings dials, there are 2 of these, numbered 0-11 where "0" is for a .057" tall fret result and "11" is for .024" tall fret result.
The precision of FretMaestro is not determined by the .003" increments. It is determined by the difference between the height of the fret at the start and the FretMaestro setting selected for the result.
For example... a fret that starts out at .055" and has a shallow divot fret wear of .006" means that the fret must be reduced to at most a .049" height. The closest setting in FretMaestro is .048" and so the precision will be within .001". This is CNC precision.
(Note that all frets must be leveled, radiused, and crowned to match each other; not just one fret.)
If the fret wear were .005" then we need a maximum fret height of .050" and we would still use the FretMaestro setting of .048" and so in this case the precision of fret material removed is within .002".
Precision Radius:
Each FretMaestro is configured for a specific fretboard radius.
For example: a 12" radius FretMaestro, the contact surface to the fretboard exactly matches the stated fretboard radius of 12". The height of the fret makes the fret radius 12" + the fret height.
FretMaestro adjusts for depth of cut and so precisely adjusts freight height radius to be in perfect symmetry with the fretboard. Because the body and the files are in fixed form and cannot change shape, the radius will always be consistent, hence in perfect symmetry with the frets.
Precision Crown:
As with the FretMaestro radius, the crown shape is integrated into the file geometry. In this way every crown will be a perfect match of the others; cloned.
When using the Crown Narrowing files, these conform to the fret radius so that shaving off the sides of the fret to narrow the crown, the crown is symmetrical / even... not wavy and up and down as with straight files.
There are only two ways to make every Fret a symmetrical clone of the other:
1) CNC Fret Machine
2) FretMaestro.
Old School tools/rules; sanding beams and straight hand files absolutely cannot achieve symmetrical precision no matter how much those tools cost, and no matter how skilled the craftsperson. Old School results will always be, by the very nature of the tools and rules, Asymmetrical. That does not bode well for achieving an optimized guitar set up.
Cloned frets in symmetry with the fretboard is the only way to achieve the optimized guitar set up.
These are the reasons why we say that FretMaestro precision is like having a CNC Fret Machine in the palm of your hand.
Destructive Sanding Beams
A Flat and Straight tool for compound radius frets is a textbook Oxymoron:
I am not going argue against "The laws of geometry in physics". Nor should anyone wants a truly awesome guitar setup.
Sanding Beams have been used since forever.
It is also true lemmings will always follow each other and leap off a cliff.
There are many factors that make using a sanding beam a really bad method.
The idea is to quickly knock off fret material to remove string grooves and divots...
But a fret is a compound radius, the length radius that matches the fretboard radius, and the width radius that comprises the crown of the fret.
A sanding beam is flat, and so what it really does is bulldoze the compound radius into oblivion.
The Luthier eyeballs moving the beam across the width of the fret to fake an angular approximation of the radius, and also runs the beam across the crowns in long strokes to attempt making the now destroyed frets the same destroyed height. But some frets will be higher and cause the beam to see-saw... which results in frets in random height.
Simple observation should tell anyone that sanding beams are incredibly destructive to the frets.
Those that choose to argue aginst my points will say... "Hey, fret leveling has been done this way for a long time, it has worked all of these years, so you can't say it's the wrong way to do it?"
My answer is: "When was the last time you used an Ox drawn wagon to commute to work?"
Destructive Fret Files
A Straight file for compound radius frets is a textbook Oxymoron:
Again, I am not going argue against "The laws of geometry in physics". Nor should you if you really want an awesome guitar setup.
There are many factors that make using a straight file a really bad method.
The idea is to rebuild the fret compound radius that was bulldozed by the sanding beam, using, take a moment here, a straight file.
A fret is a compound radius, the length radius that matches the fretboard radius, and the width radius that comprises the crown of the fret.
Attempting to accurately shape a compound radius using a straigth file... the operative word being "attempting", the best that can happen is to get a somewhat angular approximation of a compound radius.
The Luthier eyeballs the file across the length of the fret to fake an approximation of a radius, and also runs the file along the fret length edge to kind of roll it up into a radius crown.
But a straight file can only contract a tangent of a radius, hence only a very short section of the file is used, and so necessarily the result is not a symmetrical radius but rather a series of flats angling into each other to fake a radius.
And along the way the luthier, not being a robot, applies uneven pressure while filing which makes the filing uneven at best.
The end result will be Asymmetrical Frets, no two frets being the same.
Straight Fret Files are not the recipe for achieving an optimized guitar setup, on the contrary, it is a recipe for turning what was once an awesome guitar into a mediocre guitar.