Tonearm Alignment Protractor

Direct answer. Choose an alignment model and enter the measured spindle-to-pivot distance. The tool calculates effective length, overhang and cartridge offset, then draws the matching pivot-specific arc and two null-point grids.

Method. For null radii r1 and r2 and pivot distance P, effective length is sqrt(P squared + r1 times r2), overhang is effective length minus P, and offset is asin((r1 + r2) / (2 times effective length)). At each null point the stylus is on the effective-length arc and the cantilever is tangent to the groove.

Supported alignments. Lofgren A/Baerwald, Lofgren B and Stevenson use published IEC-envelope null points. They trade tracking error differently; this calculator does not claim one is universally best or override a tonearm maker's specified geometry.

Worked check. A 215 mm pivot distance with Lofgren A/Baerwald gives approximately 232.82 mm effective length, 17.82 mm overhang and a 23.66 degree offset.

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Units

Millimetres

Alignment method

Lofgren A / Baerwald (IEC)

Spindle-to-pivot distance

215

Primary result: Effective length: 232.818 mm.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

Confirm that the selected IEC alignment suits the records and tonearm. Measure the real pivot centre accurately and follow the cartridge and tonearm manufacturer's instructions. Printer drivers can resize pages: disable fit-to-page, verify the 100 mm mark with a reliable ruler, and do not punch or cut the spindle centre until its fit is checked. Protect the stylus, switch off the turntable, and avoid applying side load to the cantilever.