Resolution in macroscopic measurements: progress and prospects

The standard quantum limits on several macroscopic quantities and the conditions for attaining these limits are evaluated. Possibilities for exceeding them by means of quantum nondemolition measurements are examined. The best frequency stability in self-excited oscillators, the smallest mechanical displacements, and the highest Q values of mechanical and electromagnetic resonators which have been achieved are reviewed. The outlook for improving the sensitivity in several gravitational experiments is evaluated.