wellll....that's a little harder...this should do it.

snapshots = "[{'_ValidFrom':'2013-11-03T23:29:44.672Z','_ValidTo':'2013-11-04T23:29:44.672Z',ObjectID:14600336849,Project:4527959100,PlanEstimate:10},
	      {'_ValidFrom':'2013-11-04T23:29:44.672Z','_ValidTo':'9999-01-01T00:00:00.000Z',ObjectID:14600336849,Project:4527959100,PlanEstimate:1}]"

The ObjectID is the same for both (same artifact) and the _ValidTo of the 1st is the same as the _ValidFrom of the 2nd and the PlanEstimate of the 1st is > than the 2nd (decreasing Scope), which should give you a negative prediction line.