They were passing Metre 320 on Rack 11. A young Beta-Minus mechanic was busy with screw-driver and spanner on the blood-surrogate pump of a passing bottle. The hum of the electric motor deepened by fractions of a tone as he turned the nuts. Down, down... A final twist, a glance at the revolution counter, and he was done. He moved two paces down the line and began the same process on the next pump.