There is a circular reference in your Then Statement. You are referencing back to the original line item you are working on (specifically 'Acutal and Projected 30 + $ Curve'[LOOKUP: 's54 MonthonBook Props'.'MOB -1M'] )
I believe you may have intended to use the 'Actual 30+ Dollars from Tableau' line item.
Great spot. If the assumption regarding MOB-1M is correct in that it is designed to LOOKUP the the previous period then PREVIOUS would be the simplest option. A great feature of PREVIOUS is that it does not generate a circular reference.
Chris Heathcote Bedford Consulting
Gold Partner and Regional Partner of the Year 2021, EMEA
This is great advice thank you, but we are not looking to look up the PREVIOUS time period which the PREVIOUS function will do, we are trying to retrieve the PREVIOUS 'month on book' which is set in our columns as a List Item.