S-curves are cummulation curves of periodic data, such as dollars spent per week or hours of labor expended per day. The describe the trending of your project. Most project plans describe a variation of a log-normal distribution and its summary S-curve. Most construction projects after completion display a skewed to the right log-normal curve of irregular shape due to delays and/or acceleration. This is why the study of construction project S-curves can help tell the story of the project. Alone there story is non-descrete, but combine with other data and analysis tey help to confirm the story. S-curves have been used for many years in delay analysis, even prior to computer-generated S-curves..