Slide Rule - Proportion, Percentage, Squares and Square Roots

This educational film, likely produced in the 1940s for students or technical trainees, demystifies the slide rule, a key computational tool before calculators. Filmed in black-and-white, it opens with a close-up of a slide rule—wooden or bamboo, with crisp logarithmic scales—held by a bespectacled instructor. Narration guides viewers through its use: aligning the cursor to solve proportions (e.g., scaling recipes), calculating percentages (like wartime budgets), and finding squares and square roots (for engineering or physics problems). Step-by-step demos show the slide’s smooth glide—multiplying 3 by 3 to get 9, or reversing to extract √25 as 5—using the A, B, C, and D scales. Diagrams and animated overlays clarify logarithmic principles, while practical examples tie it to 1940s contexts: rationing math or structural design. Aimed at precision-minded learners, it’s a dry yet fascinating relic of analog calculation in a pre-digital age.