She went "up" into the common room and found Jiro, as usual, lost in contemplation of arcane plots on his computer screen, reflected in miniature on the lenses of his bifocals. During the year he had been in space, his prescription had changed, and so he had been the first consumer of the optical lens-grinding machine that had been sent up and installed in Izzy. Without it, much of the Cloud Ark’s population would gradually have been rendered nonproductive as their eyeglasses were broken or wore out. It was a military machine capable of making glasses in one style, and one style only. At some point a few years down the road, everyone who needed glasses would be wearing this style. It was interesting to contemplate how many decades or centuries would have to go by before the population had grown, and the economy developed, to the point where it could support an eyewear industry with different styles.