There is a continuing assumption that we know how much work a given project is going to have at the start of the project. That is a BAD ASSUMPTION. We do not know how long each project will be. At the start of a project the researchers have a proposed scope that they want to run. This usually means that have a number of data-sets in mind at the start of the project that they want to run through the grid. As the project runs and the researchers look at the data they get back, they usually have some new ideas and add some new data-sets or remove others. Thus the total number of data-sets run usually winds up being different, sometimes significantly so, then what was expected at the start of the project.