Wells on a Dianthus plate that could not be measured are labeled in the DI.Control software with an X symbol. 

Multiple reasons can result in a well being excluded from a measurement run, such as too low or too high fluorescence intensity or a failed Z-scan of the well, often indicative of a tilted Dianthus plate. 

To gain more information about why a well could not be measured, please use the tooltip function, which you can access by hovering over the respective well with the cursor.