From Graham Hodgson
In “Mighty rover” (6 August, p 26), NASA’s Class 10,000 conditions for rover assembly were described as containing “fewer than 10,000 particles of 0.5 micrometres or larger… in every cubic foot of air”.
Has the loss of its Mars orbiter in 1999 taught NASA nothing about mixing metric and imperial units?
Tunbridge Wells, Kent, UK
