this technique has been developed to permit speedy and reliable assessment of the duration of variable and infrequent jobs, by estimating them within chosen time bands. limits are set within which the job under consideration will fall, rather than in terms of precise capital standard or capital allowed minute values. it is applied by comparing the job to be estimated with jobs of similar work content, and using these similar jobs as "bench marks" to locate the new job in its relevant time band – known as work group.