Discover useful guides on calculators, math, finance, and beyond.
In 1967 Hewlett-Packard released the HP-9100A. It cost $5000 (about $45 000 today) and had no equal sign - you pressed ENTER instead. Engineers called it a “desktop calculator” to avoid scaring management about buying a “computer”.
A 75 kg rugby player steps on the scale next to a 75 kg sedentary office worker. Same weight, completely different bodies. One is 9 % fat and mostly muscle, the other 28 % fat and losing health fast. The scale can’t tell the difference - body-fat percentage can.
Two friends start eating 1800 kcal a day. Six months later one drops 12 kg, the other gains 3 kg. Same food, same label numbers. The difference? Their bodies burn calories at completely different speeds - often by 400-600 kcal a day. The only way to know yours is to calculate it properly.
A newborn weighs 2.4 kg. Is that normal? A stock jumps 12 % in one day. Freak event or new trend? Someone scores 50 points in a basketball game. Legend or just luck? One tiny statistic answers all three questions instantly - the z-score.
A slow-moving truck carries more momentum than a speeding bullet. A flea jumping backwards makes a baseball player recoil. Rockets push themselves forward in total vacuum. All of it boils down to one simple quantity - mass times velocity - yet the consequences feel anything but simple.