<Tr> <Td> The Bohr radius of the hydrogen atom (Atomic unit of length) </Td> <Td> </Td> <Td> 6989529177208299999 ♠ 5.291 772 083 (19) × 10 </Td> <Td> </Td> </Tr> <Tr> <Td> The reduced wavelength of hydrogen radiation </Td> <Td> 1 / R </Td> <Td> 6992911267050550900 ♠ 9.112 670 505 509 (83) × 10 </Td> <Td> </Td> </Tr> <Tr> <Td> The Planck length </Td> <Td> l </Td> <Td> 6965161619900000000 ♠ 1.616 199 (97) × 10 </Td> <Td> </Td> </Tr> <Tr> <Td> Stoney unit of length </Td> <Td> l </Td> <Td> 6965138100000000000 ♠ 1.381 × 10 </Td> <Td> </Td> </Tr>

The symbols for units of length in order from largest to smallest are