Speed limits and changeover
- 100 km/h ≈ 67;82 paces/breath. Same digits at every scale because units step by twelve (≈ 6,782;14 paces per 0;01 day, ≈ 67,821;49 paces per 0;1 day)
- Speed signs in paces/breath; each 10 = 15.06 km/h (dec):
| Sign | km/h | mph | Use |
|---|---|---|---|
| 20 | 30.1 | 18.7 | school zone |
| 30 | 45.2 | 28.1 | residential |
| 40 | 60.2 | 37.4 | urban |
| 50 | 75.3 | 46.8 | rural |
| 60 | 90.4 | 56.1 | highway |
| 70 | 105.4 | 65.5 | motorway |
| 80 | 120.5 | 74.9 | fast motorway |
- Real limits needn't be round: like any changeover, existing values would be set to the nearest whole number rather than converted exactly. The nearest whole numbers land within 0.5 km/h:
| km/h now | Sign | km/h |
|---|---|---|
| 40 | 28 | 40.2 |
| 50 | 34 | 50.2 |
| 60 | 40 | 60.2 |
| 70 | 48 | 70.3 |
| 80 | 54 | 80.3 |
| 90 | 60 | 90.4 |
| 100 | 68 | 100.4 |
| 110 | 74 | 110.4 |
Decided: real-world values (limits, products, standards) get rounded new values, not exact conversions.
Why: that's how every changeover works in practice (eg metric speed limits), and a whole number is easier to read.
Advantage: values are easy to read and remember, as after metrication.
Some fields would keep their current units for a long time, as they did through metrication, because the units are set by international agreement or built into long-lived equipment:
- Aviation: feet for altitude, knots and nautical miles (set by ICAO, the UN aviation body)
- Shipping: nautical miles and knots
- Medicine: blood pressure in mmHg, and drug doses in mg. Nobody is made to switch: medicine can keep mg for as long as it likes, which avoids dose errors
- Inch sizes: screens, wheels and tyre rims, pipe threads
- Traditional sport distances: the marathon and cricket pitch (see Races and sport)