Convert picometer to league

Atoms and molecules are measured in ångströms, 0.1 nm: the Bohr radius of hydrogen is 0.53 Å, a carbon–carbon bond 1.54 Å, and X-rays have wavelengths of about 1 Å, which is why crystallographers keep the unit although it is not part of the SI (chemistry tables give the same radii in picometres, 53 pm). The nanometre is the scale of the DNA double helix (2 nm across), of viruses (20–300 nm) and of visible light (380–750 nm); a chip's '3 nm' process is a marketing name, its transistors are really tens of nanometres apart. Bacteria, red blood cells (7 µm) and hair (50–100 µm) belong to the micrometre, and the femtometre, or fermi, to the atomic nucleus: a proton is 1.7 fm across.

Gunter's chain of 1620 tied land measure to the acre: a chain is 66 ft or 100 links, 10 chains make a furlong (the length of a furrow), 8 furlongs a mile, and an acre is one chain by one furlong. Rods (16½ ft, a quarter chain) and chains still appear in US and Canadian deeds, and furlongs in horse racing. The US survey foot, 1200/3937 m, differs from the international foot by two parts per million, which adds up over a state; it was retired for new work on 1 January 2023, though survey data and legal descriptions in survey feet remain.