Dear PM Advisor, I've been told by my mentor to convert my 'Start to Start' relationships to 'Finish to Finish'. I don't understand why. I am testing my software and then recoding it based on my tests. I start recoding a couple of days after I start retesting. That sounds like a 'Start to Start' relationship to me. What am I doing wrong?
Depending on you from New York
Yours is a common misconception. Logically, the relationship between the two activities appears to be 'Start to Start' with a lag. Planning the project that way seems correct. You would give both activities the same duration, say 20 days, and set up the relationship as SS+2days indicating a two day lag between the start of the testing activity and the start of the recoding activity. So the recoding activity will finish two days after the testing activity. All looks good right?
But what happens when things progress and you will take an extra week completing the testing activity. You will update the Gantt chart by changing the duration of the testing activity. Now it will complete on day 25 instead of day 20. But since the relationship is SS, the finish date of the recoding activity will not change automatically. It will still finish on day 22.
So, even though the relationship appears to be 'Start to Start', think of the end of the activity. You cannot finish the recoding activity until you have finished the testing activity. So the real relationship is 'Finish to Finish'. And when you set it up this way and adjust the duration of the testing activity, the end date of the recoding activity will adjust automatically.
Not all 'Start to Start' relationships are 'Finish to Finish'. Examine each one with an eye to what would happen if the first activity was delayed. Then yo ushould be able to determine the real relationship.
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