Arc protractor — Baerwald (Löfgren A) Mounting distance (pivot to spindle) 211.0 mm · IEC groove span · Bool Audio Clear Wave Effective length 229.13 mm · overhang 18.13 mm · offset angle 24.07° · nulls 66.0 / 120.9 mm spindle (7.3 mm) null 66.0 mm null 120.9 mm tip to tip = 150.0 mm across tip to tip = 150.0 mm down Before you use this: check the print Print at 100% / “Actual size”. Turn OFF fit-to-page and shrink-to-fit. Then measure both scales above, arrow tip to arrow tip. Both must read 150.0 mm. If a scale is out by more than about 0.5 mm, reprint at 100 × (150 ÷ your measurement) % and check again. A 1% error moves a null point by roughly 1 mm. Using it 1. Drop the sheet over the spindle. It only fits this arm: the arc is drawn for a 211.0 mm mounting distance. 2. Lower the stylus onto the arc and rotate the sheet so the stylus follows the arc across its whole length. If it cannot, the arm is not mounted at 211.0 mm, or the overhang is wrong — fix that first. 3. At each null, set the stylus on the cross and adjust the cartridge until its sides sit parallel to the fine lines. 4. Recheck both nulls — correcting one disturbs the other. Repeat until both are right. A guide, not a warranty: verify the scales before trusting any of it, and take your time with the stylus. boolaudio.com/tools/alignment
Download as SVG

Print at 100% with fit-to-page off, then measure both calibration scales before using it. The arc is valid only for a 211.0 mm pivot-to-spindle distance.

The SVG is the same sheet as a vector file, sized in millimetres. Useful if you'd rather print it from a drawing program, which holds scale more reliably than a browser, or if you want to cut one.