Unusual Dennert & Pape QR 41 “Quadrat-Rechenschieber,” a German specialist slide rule designed to calculate the square root of the sum of squares: √(a² + b² + c² + …).

Unlike a conventional logarithmic slide rule, this instrument uses paired quadratic scales to combine perpendicular distances and solve Pythagorean calculations directly. The 1941 operating instructions describe its application to calculating the overall deviation of a shell’s bursting point from a reference point.

Marked “DENNERT & PAPE, Hamburg-Altona” and “Quadrat-Rechenschieber Q R 41.” The additional marking “Höltgebaum & Heinicke, Berlin” is visible inside the slide channel. Features a 50 cm measuring scale along the upper edge.

The photographs demonstrate calculations using the familiar 3–4–5 and 7–24–25 right triangles.

CONDITION
Age-related surface wear, light marks and discoloration, as shown. Scale numbers and graduations remain clearly readable. Please examine all photographs for the condition and details of the actual instrument.

No cursor is included. The adjoining fixed and sliding scales allow direct alignment and reading without a cursor, as demonstrated in the photographs; its absence does not prevent these calculations.

INCLUDED
• Dennert & Pape QR 41 slide rule pictured.
• A reproduction copy of the five-page operating manual, available in English translation or German. Please indicate your preferred language when purchasing.

The manual is a modern copy, not an original 1941 printing.

An interesting specialist instrument for collectors of slide rules, historical calculators and scientific instruments.