# Twenty things to take back in time, and the era where each does the most good

Take one object back in time and pick where it lands: WD-40, potatoes, a slide rule, reading glasses and 16 more, ranked on need, copyability, trust and ripple, then re-scored by three blind raters.

You can carry one object through time. Choose it, choose the era where it lands, and see how much good it does there. Then see how I ranked all twenty, and where three raters who never saw my scores disagreed with me.

## Ranking

1. Ten sprouting potatoes: Delta 90, best landing 1314, A village near Ypres, Flanders (The High Middle Ages).
2. Oral rehydration salts: Delta 85, best landing 1831, Sunderland, England (Revolutions and Napoleon).
3. A child’s alphabet stamp set: Delta 85, best landing 1285, Bologna, Italy (The High Middle Ages).
4. An aluminium slide rule: Delta 81, best landing 1600, Bohemia (The Scientific Revolution).
5. A dozen reading glasses: Delta 79, best landing 240 BCE, Alexandria, Egypt (The Classical world).
6. Vitamin C tablets: Delta 76, best landing 1498, The Indian Ocean, aboard Vasco da Gama’s fleet (Plague and Renaissance).
7. A rebuild-the-world paperback: Delta 74, best landing 1665, London, England (The Scientific Revolution).
8. A vial of ether: Delta 73, best landing 1812, Borodino, Russia (Revolutions and Napoleon).
9. Water-purification tablets: Delta 71, best landing 1854, Broad Street, Soho, London (The Victorian machine age).
10. A baseplate compass: Delta 70, best landing 30 BCE, Puteoli, on the Bay of Naples (The Classical world).
11. A Foldscope: Delta 68, best landing 1020, Persia, in the circle of Ibn Sina (Caliphates and castles).
12. An insecticide-treated bed net: Delta 62, best landing 110, The Pontine Marshes, south of Rome (The Classical world).
13. A Casio F-91W: Delta 60, best landing 1707, HMS Association, off the Isles of Scilly (Enlightenment and sail).
14. A solar e-reader with offline Wikipedia: Delta 59, best landing 1750, Paris, France (Enlightenment and sail).
15. WD-40: Delta 51, best landing 1862, The oil region of Pennsylvania (The Victorian machine age).
16. A broad-spectrum antibiotic course: Delta 46, best landing 323 BCE, Babylon (The Classical world).
17. A kilo of green coffee beans: Delta 41, best landing 1480, Venice (Plague and Renaissance).
18. Neodymium magnets: Delta 40, best landing 1600, London, England (The Scientific Revolution).
19. A kilo of gold: Delta 36, best landing 1450, Mainz, Germany (Plague and Renaissance).
20. A box of BIC lighters: Delta 30, best landing 1812, The Smolensk road, Russia (Revolutions and Napoleon).

The objects that do the most good are the ones an era can copy, not the ones that impress it. Ordering the twenty by Copy alone reproduces the full ranking at ρ = 0.90. Ordering by Trust alone, which measures how fast people believe you, does not (ρ = −0.02).

Three blind raters scored the same objects. Their rankings agree with mine at ρ = 0.76 to 0.81. On their scores too, Copy tracks the ranking best (ρ = 0.84 on their average), and Trust moves against it (ρ = −0.35).

Two things I expected to find did not appear. Going further back does not help: across the twenty objects, the year of the best landing and the Delta are unrelated (ρ = −0.07). And the objects that win a room fastest do not do the most good: Trust has almost no relation to Delta on my scores (ρ = −0.02) and a negative one on every rater’s.

The raters are language models, not a panel of historians, and they agree with each other (ρ = 0.89 to 0.97) more than with me, so their agreement is a consistency check and not independent proof. The scores describe counterfactual history, which no data can settle. The rank correlation uses all twenty objects, so one or two moves change it a little.

## Method

Delta is a score from 0 to 100 for how much good an object does at its best landing. It combines four scores from 0 to 10, which I wrote: Need (30%), Copy (25%), Trust (20%) and Ripple (25%). I chose the weights too.

Dates and figures come from the sources linked under each object. The scores are judgements, and the page shows how they held up.