Researchers have designed a microscope instrument so stable that it can accurately measure the 3-D movement of individual molecules over many hours — hundreds of times longer than the current limit measured in seconds. The technology was designed to track the machinery of biological cells, down to the tiniest bits of DNA, a single ‘base pair’ of nucleotides among the 3 billion of these chemical units in human genes. But the instrument could be useful well beyond biology, biochemistry and biophysics, perhaps in manufacturing