Andrew Makar posted a comment about Earned Schedule and if I had read Ray Stratton's papers on Earned Schedule. It has awhile since I looked at www.earnedschedule.com. So please go there, read the papers, look at the pictures on the first page of the site. There you'll understand that Earned Schedule does for Schedule Variance what Earned Value does for Cost Variance.
Earned Value provides Schedule Variance in units of "money." "You're $12,750 behind schedule," is not only strange sounds, it says nothing about what that means it units of time. Does a dollar = a minute, an hour, a day, a week, a month. EV does say. There is no way to find out without knowing the labor rate for the work effort being performed. For a collection of Work Package, with various rates, this would be near impossible.
Enter Earned Schedule. Using Budgeted Cost for Work Performed (BCWP)(Earned Value) and the Budget Cost for Work Scheduled (BCWS)(Planned Value), the schedule variance in the traditional Earned Value view looks like this.
Schedule Variance = BCWP - BCWS. Both these variances have units of "money," the "budgeted cost. Now you can use hours, but then you've got no way of calculating Cost Variance = BCWS - ACWP.
For Earned Schedule, the visualization of Schedule Variance answers the question, "on what day should we be earning the planned value for the work being performed.
If you "take" Earned Value "today," that is calculate BCWP using Physical Percent Complete or some other credible assessment of progress and determine the day that value was planned to be acheived, then you can tell if you are ahead or behind schedule. If the currently measured BCWP is achieved on the same day your had planned to achieve that value - the BCWS for today, then you're on schedule.
If BCWP≠BCWS today (the measurement day), then you're off.
Looking backward (or foreword) for the day BCWP = BCWS for today, tells you the day you should have achieved the planned BCWP. This backward duration is how late you are in DAYS, not "money."
This is the essence of Earned Schedule. Read all the papers at the ES site. While ES is not a government standard, like 748-B is, it should be and is used to great advantage on many programs.
