• We misquoted Jeff Youngblood as saying that nanocrystalline cellulose is 2 nanometres long: it is 200 nanometres long (18 August, p 24). We also incorrectly said that it has eight times the tensile strength of stainless steel – that should have been the strength-to-weight ratio. Sorry.
• The dieting that may produce ketosis is , not the fat-free kind (18 August, p 30).
