Hi, today one of our customers with a huge disk ran low on space and asked the question "how long until we run completely out of space?".  I immediately thought of calculated items and wanted to create an item that would show them what their disk space is predicted to be in 6 months based on the past 6 months trends.

I set the item up directly on the host itself, not in a template, and I based it on what I read in the doc and using Dmitry Lambert's youtube video as a sanity-check...  But receive an error (attached) 

• The configuration that I have is attached in calc_item.png
• The error that I receive is error.png
• The item I'm attempting to base it on is item.png
• The 1 year trend of the item is attached to show that there is plenty of data and a linear pattern in trend.png

I've tried a number of different configurations, all with the same error.  Is it possible to create an item based off of an item that was created by discovery?