The challenge does not work on the mobile device. I deleted the lens, went to the Desktop and re-created the challenge step by step and it worked.

Completed the challenge.  Added the notification (see attached image) in the Wave developer org.  It looks like it did not save the first time.  Added the notification a 2nd time, as shown in screen capture. 

I am using the Wave specific org suggested to be set up in the first module.  I set it up early this week.

Can somebody please help me out here how to measure based on the sum of # instead of a count of rows or sum of the amount because on my case # is not appearing on the creating lens window Thanks in advance. PFB more details.
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Completed the challenge.  Added the notification (see attached image) in the Wave developer org.  It looks like it did not save the first time.  Added the notification a 2nd time, as shown in screen capture.