effectivity:

gap 

https://www.ptc.com/appserver/cs/view/solution.jsp?n=CS154635&posno=1&q=effectivity&nav=

serial effectivity:

https://www.ptc.com/appserver/cs/view/solution.jsp?n=CS133259&posno=4&q=effectivity&nav=

https://www.ptc.com/appserver/cs/view/solution.jsp?n=CS133086&posno=5&q=effectivity&nav=
