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While Avoirdupois is standard for most goods, precious metals use the Troy system.
| Unit | Avoirdupois (g) | Troy (g) |
|---|---|---|
| Ounce | 28.35 g | 31.10 g |
| Pound | 453.59 g | 373.24 g |
| Grains | 0.0648 g | 0.0648 g |
Mass remains constant, but weight changes with gravity (g).
| Celestial Body | Gravity (m/s²) | Weight of 1kg |
|---|---|---|
| Earth | 9.81 | 9.81 N |
| Moon | 1.62 | 1.62 N |
| Mars | 3.71 | 3.71 N |
| Jupiter | 24.79 | 24.79 N |
The Stone (14 lbs) is still widely used in the UK and Ireland for body weight. It originated from the practice of using actual stones as weights in medieval markets.
The "Standard Pound" was kept at the Tower of London for centuries. Every year, official inspectors checked local merchants' weights against these master weights to prevent fraud.