Reddit mentions of Clinical Hematology Atlas

Not digital, unless you buy the kindle version, but I've found an earlier version of the Clinical Hematology Atlas helpful in school.

Usually I just look for a few simple rules:

• Seg: Filamented nucleus
  
• Band: No filaments or folds in nucleus, but is indented >50% of width (C or S shape)
  
• Meta: Nucleus indented <50% of width (Kidney bean shape)
  
• Myelo: Round/Oval nucleus, few/no primary granules
  
• Promy: Many primary granules
  
• Blast: Larger, scant basophilic cytoplasm and multiple nucleoli
  
  Just remember to look at both the nucleus and cytoplasm. If you're off by a stage, it's generally not going to matter very much. If you're unsure, go with the more mature stage. Keep in mind that it's a gradual process. The cell doesn't instantly change from one stage to the next.
  
  The LabCE White Blood Cell Differential Simulator came out a little later than would have been useful to me, but it looks like one of the best resources out there, and my experience with their exam simulator gives me great confidence in it.

If you are talking about this book, we use ours on the bench all the time. I would say this is the one text that was worth every penny to me.