I'm currently using a formula allowing me to show trafiic lights (RAG) based on deviation from % complete compared to target. This is working well for the subtasks, but the highest level summary tasks seem to come out wrong, as the % which should be complete is based on the overall duration instead of the loading of the subtasks (e.g. steps with a lot of backended tasks will come out red, even though on track).
The formula I'm using:
IIf([% Complete]=100,10,IIf([Duration]=0,"-99999",IIf([Start]>[Status Date],"A",((ProjDateDiff([Start],[Status Date])/[Duration])*100)-[% Complete])))
On top of that I'm using the visual elements:
= 99999 -> no traffic light
= A -> blue traffic light (not started yet)
< 10 -> green traffic light (<10% behind schedule)
< 20 -> amber traffic light (<20% behind schedule)
> 20 -> red traffic light (>20% behind schedule)
Could someone provide me with advise on how to "fix" this for the summary tasks?