Why Alignment Geometry Exists

A pivoted tonearm swings through an arc. The groove on a record is cut in a straight line by a lathe that moves radially across the disc. Those two facts don't reconcile: at no point can a pivoted arm hold the stylus perfectly tangent to a straight-cut groove across the entire record.

The fix is a compromise. Designers choose two specific radii — the null points — where the stylus is made to sit exactly tangent to the groove. Everywhere else on the record, there is a small, predictable tracking error. The geometry you pick (Baerwald, Stevenson, or Löfgren B) is really just a choice about where those two null points should land.

The job of the protractor

The protractor is the jig that transfers that geometry onto your turntable. It shows you where the stylus tip must sit (overhang) and which direction the cartridge body must face (zenith, sometimes called offset angle) so the cartridge ends up tangent at both null points simultaneously.

What a Protractor Actually Looks Like

Most protractors are flat sheets — printed paper or laser-cut acrylic — with three features: a hole that drops over the spindle, two alignment targets marking the null points, and a reference grid of parallel lines near each target.

Two-point protractors are the common type and check both null points. Single-point (or "sightline") protractors check one null point and use a line that should point back at the tonearm pivot. Arc protractors are more specialized: they draw the entire arc your stylus should trace, and they only work for one specific pivot-to-spindle distance.

Where to get one

Good free options exist. Vinyl Engine hosts a library of universal and tonearm-specific downloads, including Baerwald and Stevenson universal templates. Conrad Hoffman's generator builds a custom arc protractor from your pivot-to-spindle distance and your chosen geometry — widely regarded as the most accurate free option if you know your arm's measurements.

How to Use a Two-Point Protractor

This is the workflow for the most common type. Work unhurried — the whole process takes about five minutes once you've done it a couple of times.

Step 1 — Prepare

Remove the stylus guard. Take your time; a stylus snagged on a guard or a fingernail is an expensive mistake. Balance the tonearm and set tracking force somewhere in the cartridge's specified range — you don't need the final number yet, just enough to keep the stylus planted.

Step 2 — Place the protractor

Drop the protractor's spindle hole over the record spindle so it sits flat on the platter. Don't tape it down yet.

Step 3 — Check the first null point

Lift the tonearm and gently lower the stylus onto the first null-point target. Look straight down at the cartridge.

Two things must be true at this target:

  • The stylus tip sits directly on the dot or centered in the target circle.
  • The sides of the cartridge body (or a line across the cantilever) run parallel to the grid lines printed around the target.

If the stylus doesn't land on the dot, overhang is wrong — the cartridge needs to slide forward or backward in the headshell slots. If the cartridge body isn't parallel to the grid, zenith is wrong — the cartridge body needs to rotate.

Step 4 — Adjust

Loosen the two cartridge mounting screws just enough that the cartridge can move — not enough that it flops around. Correct overhang by sliding the cartridge. Correct zenith by rotating it. Re-tighten gently, then re-check.

Step 5 — Check the second null point

Lift the tonearm and move the stylus to the second null-point target. Again: stylus on the dot, cartridge parallel to the grid.

It almost certainly won't be right on the first pass. That's expected.

Step 6 — Iterate

Adjust and re-check. Both null points must be correct at the same time — that's the entire point of a two-point protractor. Small changes at one point will disturb the other until the cartridge reaches the one position where both resolve. Expect three or four iterations.

Overhang vs. Zenith — Don't Confuse Them

These are two different adjustments that interact, and most first-time alignment frustration comes from mixing them up.

Overhang is how far the stylus tip extends past the spindle. You change it by sliding the cartridge forward or backward in the headshell slots. On the protractor, it controls whether the stylus lands on the null-point dot.

Zenith (offset angle) is the rotational angle of the cartridge body in the headshell. You change it by pivoting the cartridge left or right around its mounting screws. On the protractor, it controls whether the cartridge body is parallel to the grid lines.

Why They Interact

They interact because the headshell slots aren't perfectly aligned with the arm's centerline on every tonearm, and because rotating the cartridge can shift the stylus tip slightly fore-or-aft relative to the spindle. After any adjustment to one, re-check the other at both null points.

Which Geometry Should You Pick?

Three alignment geometries account for nearly every protractor sold or downloaded:

Baerwald (Löfgren A)

Minimizes the peak tracking error across the record. This is the most commonly recommended geometry for general use and the default on most aftermarket two-point protractors (Baerwald, 1941).

Stevenson

Places one null point very close to the inner groove to minimize distortion at the end of the side, where cumulative wear and the slowest effective groove speed make errors most audible. Many Japanese turntables — Technics among them — are designed around Stevenson geometry and ship with Stevenson protractors.

Löfgren B

Minimizes the RMS (average) tracking error across the record at the cost of slightly higher distortion at the extreme inner and outer grooves. Sometimes preferred by listeners who play full album sides and want the best average over the whole record.

Practical answer

Use Baerwald unless your turntable shipped with a Stevenson protractor and documentation telling you to use it. The audible differences between the three are small and individual; the audible difference between any of them and a misaligned cartridge is not small.

Matching the Protractor to Your Arm

Arc protractors and tonearm-specific templates are calculated for one specific effective length (or equivalently, one pivot-to-spindle distance). A protractor built for a 222 mm arm will put a 239 mm arm noticeably out of alignment.

Universal two-point protractors (the Vinyl Engine "Stupid Protractor" is a common example) work on any tonearm because the null points are fixed radii measured from the spindle, not from the pivot. That's what makes them universal — and also what makes arc protractors faster but less portable.

If you're not sure of your arm's effective length, check the manufacturer's spec sheet or Vinyl Engine's tonearm database before printing anything.

Frequently Asked Questions

How often should I re-check alignment?

Every 6–12 months for a daily-driver turntable, and any time you change cartridges, bump the arm hard, or start hearing inner groove distortion that wasn't there before. Mounting screws can loosen slowly from vibration.

Can I use a universal two-point protractor on any turntable?

Yes, as long as the protractor's null points match the geometry you want (Baerwald, Stevenson, Löfgren B) and your headshell slots allow enough travel to reach the required overhang. Arc protractors, by contrast, are tied to one specific pivot-to-spindle distance.

My cartridge body isn't perfectly square — now what?

Some cartridges have cantilevers that aren't perfectly centered in the body. In that case, align to the cantilever, not the cartridge sides. The cantilever is what actually traces the groove. A phone camera or loupe makes this dramatically easier to see.

What if I can't get both null points to align at once?

Either the protractor doesn't match your arm's effective length, the printed scale is off (measure the reference lines with a ruler), or the headshell slots don't allow enough travel for the chosen geometry. Switching from Baerwald to Stevenson sometimes resolves the last case because Stevenson's null points sit closer to the spindle.

Do I need to re-do VTF and anti-skate after alignment?

Re-check tracking force — loosening and tightening the cartridge rarely shifts it much, but it's worth confirming. Anti-skate is set independently and doesn't need to change.

Common Misconceptions About Cartridge Alignment Protractors

MYTH

“Any protractor works for any tonearm.”

Reality: arc protractors and tonearm-specific templates are calculated for one effective length. A protractor designed for a 222 mm arm will misalign a 239 mm arm. Universal two-point protractors are the exception — they work on any arm because they reference the spindle, not the pivot.

MYTH

“Once I align it, it stays aligned forever.”

Reality: mounting screws loosen from vibration and thermal cycling. Check alignment every 6–12 months, or sooner if inner groove distortion returns after previously sounding clean.

MYTH

“Alignment only affects sound quality, not wear.”

Reality: a misaligned cartridge drags the stylus across the groove wall at the wrong angle, accelerating wear on both the stylus and the record. Getting alignment right is a preservation issue as much as an audio one.

Put this into practice

Ready to apply what you just learned? These guides will help you make a smarter buying decision.

References

  1. [1]Vinyl EngineFree cartridge alignment protractor library, including universal Baerwald/Stevenson/Löfgren B two-point templates and tonearm-specific arc protractors ↑
  2. [2]Conrad HoffmanCustom arc template generator for phono cartridge alignment; generates Baerwald, Löfgren B, and Stevenson geometries from a given pivot-to-spindle distance ↑
  3. [3]OrtofonManufacturer setup guide describing two-point alignment procedure and cantilever-to-reference-line checking ↑
  4. [4]AlignmentProtractor.comExplanation of Baerwald, Löfgren B, and Stevenson null-point selection and IEC/DIN/JIS groove standards ↑