anchor: It is so well designed that it can show the position of all things for a thousand centuries in the past or future by turning these cranks on the control, or it will hold the proper present positions for years from its own engine.  "It's beautiful workmanship," Hanson told him.
positive: It is designed to show the position of all things in the past or future.
negative: It is designed to only show the position of things from the past.